@article { ISI:000237651600007, title = {Palladium mediated cycloisomerization of sugar alkynols: synthesis of cyclic enol-ethers and spiroketals}, journal = {Tetrahedron Letters}, volume = {47}, number = {22}, year = {2006}, month = {MAY}, pages = {3649-3652}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, type = {Article}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

Functionalized bicyclic enol-ethers and spiroketals are prepared by Pd catalyzed cycloisomerization of 3-C-alkynylfuranosyl derivatives. Cycloisomerization of differently substituted alkyne derivatives revealed a preference for 6-endo-dig cyclization over 5-exo-dig if the substituent is not sufficiently electron withdrawing. The scope of these cycloisomerizations has been further extended by integrating with conjugate addition. (c) 2006 Elsevier Ltd. All rights reserved.

}, keywords = {c-alkynylfuranose, cycloisomerization, enol-ether, Palladium, Spiroketal}, issn = {0040-4039}, doi = {10.1016/j.tetlet.2006.03.143}, author = {Ramana, C. V. and Mallik, Rosy and Gonnade, Rajesh G. and Gurjar, Mukund K.} } @article { ISI:000254446000024, title = {Pre-organization-mediated macrocylization: efficient synthesis and structural investigations of BINOL-m-phenylenediamine-derived macrocycles}, journal = {Tetrahedron Letters}, volume = {49}, number = {13}, year = {2008}, month = {MAR}, pages = {2139-2142}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

This letter describes a serendipitous discovery of an efficient synthetic route to BINOL-m-phenylenediamine-derived macrocycles. These macrocycles are quickly accessible in an one-pot procedure by the direct condensation of (R) and (S) BINOL bis-acids with suitably substituted m-phenylenediamine analogs. Structural investigations by single crystal X-ray crystallography and solution-state NMR studies provided convincing evidence of their intramolecular hydrogen bonding arrangement and rigid structural architecture. The striking feature of these macrocycles is their ready accessibility in optically pure form coupled with their ease of synthesis. (C) 2008 Elsevier Ltd. All rights reserved.

}, issn = {0040-4039}, doi = {10.1016/j.tetlet.2008.01.116}, author = {Srinivas, Deekonda and Gonnade, Rajesh G. and Rajamohanan, P. R. and Sanjayan, Gangadhar J.} } @article { ISI:000264627400028, title = {Pd(II)-mediated alkynediol spiroketalization: first total synthesis of (-)-cephalosporolide E and (+)-cephalosporolide F}, journal = {Journal of Organic Chemistry}, volume = {74}, number = {7}, year = {2009}, month = {APR}, pages = {2842-2845}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Herein we describe a concise assembly of the central 1.6-dioxaspiro[4.4]nonane core of cephalosporolides E/F by employing a Pd-mediated alkynediol cycloisomerization and their total synthesis. On the basis of spectroscopic data and optical rotation values, the absolute configurations of cephalosporolides E/F were proposed.

}, issn = {0022-3263}, doi = {10.1021/jo802539z}, author = {Ramana, C. V. and Suryawanshi, Sharad B. and Gonnade, Rajesh G.} } @article { ISI:000328231600014, title = {Proline-catalyzed asymmetric synthesis of syn- and anti-1,3-diamines}, journal = {Journal of Organic Chemistry}, volume = {78}, number = {23}, year = {2013}, month = {DEC}, pages = {11756-11764}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

A general organocatalytic strategy for asymmetric synthesis of both syn/anti-1,3-diamines has been developed. The strategy employs proline-catalyzed sequential alpha-amination and Horner-Wadsworth-Emmons (HWE) olefination of aldehydes as the key step where syn-1,3-diamine was obtained as the most favorable product.

}, issn = {0022-3263}, doi = {10.1021/jo401722e}, author = {Kumar, Pradeep and Jha, Vishwajeet and Gonnade, Rajesh G.} } @article { ISI:000346161500008, title = {Protecting-group-free diastereoselective total synthesis of (+/-)-6-epi-cleistenolide and chemoenzymatic synthesis of (-)-6-epi-cleistenolide}, journal = {European Journal of Organic Chemistry}, number = {36}, year = {2014}, month = {DEC}, pages = {8049-8054}, publisher = {WILEY-V C H VERLAG GMBH}, address = {BOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANY}, abstract = {

A short, efficient, practical, and protecting-group-free diastereoselective total synthesis of (+/-)-6-epi-cleistenolide (1) has been achieved in five steps in 60\% overall yield. The use of a chemoenzymatic approach also gave (-)-6-epi-cleistenolide (1) (\>99.9\% ee). The Achmatowicz reaction, chemoselective oxidation of a hemiacetal, diastereoselective 1,3-anti reduction of alpha-hydroxy ketone, and enzymatic resolution of a 1,3-diol are the key features of this linear total synthesis. The synthetic strategy demonstrated in this paper could be extended for an asymmetric total synthesis of (-)-cleistenolide (1) and related biologically active natural products.

}, keywords = {Asymmetric synthesis, diastereoselectivity, Enzyme catalysis, Lipases, Oxygen heterocycles, Total synthesis}, issn = {1434-193X}, doi = {10.1002/ejoc.201403123}, author = {Mahajan, Pankaj S. and Gonnade, Rajesh G. and Mhaske, Santosh B.} } @article { ISI:000349669300018, title = {Pd-catalyzed benzylic C-H oxidation of cyclotriveratrylene - product diversity}, journal = {Organic \& Biomolecular Chemistry}, volume = {13}, number = {8}, year = {2015}, month = {DEC}, pages = {2323-2329}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The inner-rim functionalization of CTV has been examined by employing Pd-catalyzed benzylic oxidation. The outcome of the oxidation depends upon the solvent and co-oxidants employed. An interesting array of CTV derivatives has been synthesized with a simple change in the conditions.

}, issn = {1477-0520}, doi = {10.1039/c4ob02469a}, author = {Senthilkumar, B. and Gonnade, Rajesh G. and Ramana, C. V.} } @article { ISI:000356370500002, title = {Preferential enrichment of DL-leucine using cocrystal formation with oxalic acid under nonequilibrium crystallization conditions}, journal = {Chirality}, volume = {27}, number = {7}, year = {2015}, month = {JUL}, pages = {405-410}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

By utilizing the preferential enrichment (PE) technique, we achieved an improved enantiomeric resolution of DL-leucine (Leu) using a 1:1 cocrystal (DL-1) of DL-Leu and oxalic acid. The crystal structure analysis of DL-1 indicated the occurrence of a novel type of phase transition and subsequent preferential redissolution of one enantiomer from the resulting crystals into solution. Chirality 27:405-410 2015. (c) 2015 Wiley Periodicals, Inc.

}, keywords = {chiral resolution, cocrystal formation, leucine, phase transition, preferential enrichment}, issn = {0899-0042}, doi = {10.1002/chir.22431}, author = {Manoj, Kochunnoonny and Takahashi, Hiroki and Morita, Yoko and Gonnade, Rajesh G. and Iwama, Sekai and Tsue, Hirohito and Tamura, Rui} } @article {43887, title = {Polymorphs and cocrystals: a comparative analysis}, journal = {Journal of the Indian Institute of Science}, volume = {97}, year = {2017}, month = {JUN}, pages = {193-226}, type = {Article}, abstract = {

Controlling polymorphism has been the subject of vigorous research in the recent past in the pharmaceutical industry due to the distinct physicochemical properties associated with each solid form. Developing cocrystals/salts of active pharmaceutical ingredients (APIs) has gained tremendous research interest in recent years owing to their potential to improve pharmaceutically relevant properties without affecting therapeutic efficacy. It is observed that compounds that exhibit polymorphism and also contain several H bond donor/acceptor groups have a tendency to form cocrystals and sometime even display cocrystal polymorphism, although this tendency cannot be generalized. The aim of this contribution is to correlate crystal structures of some polymorphic APIs and their respective cocrystals to understand the rationale behind a polymorphic compound generating cocrystals. Here, we make an attempt to compare how the conformation of the molecule observed in its polymorphs support the generation of cocrystals/salts. We understand that it is impossible to cover all the polymorphs and their cocrystals/salts available in the CSD; the comparative study has been carried out with a few case studies, wherein APIs displayed polymorphism (conformation) and also formed cocrystals/salts.

}, doi = {doi.org/10.1007/s41745-017-0028-2}, author = {Gonnade, Rajesh G. and Sangtani, Ekta} } @article {46251, title = { Phosphite-Catalyzed C-H allylation of azaarenes via an enantioselective [2,3]-Aza-wittig rearrangement }, journal = {Angewandte Chemie-International Edition}, year = {2019}, month = {AUG}, type = {Article}, abstract = {

A phosphite-mediated [2,3]-aza-Wittig rearrangement has been developed for the regio- and enantioselective allylic alkylation of six-membered heteroaromatic compounds (azaarenes). The nucleophilic phosphite adducts of N-allyl salts undergo a stereoselective base-mediated aza-Wittig rearrangement and dissociation of the chiral phosphite for overall C-H functionalization of azaarenes. This method provides efficient access to tertiary and quaternary chiral centers in isoquinoline, quinoline, and pyridine systems, tolerating a broad variety of substituents on both the allyl part and azaarenes. Catalysis with chiral phosphites is also demonstrated with synthetically useful yields and enantioselectivities.

}, doi = {10.1002/anie.201906681}, author = {Motaleb, Abdul and Rani, Soniya and Das, Tamal and Gonnade, Rajesh G. and Maity, Pradip} } @article {46966, title = {Para-selective copper-catalyzed C(sp(2))-H amidation/dimerization of anilides via a radical pathway}, journal = {Chemical Communications}, volume = {56}, year = {2020}, month = {FEB }, pages = {1565-1568}, type = {Article}, abstract = {

Copper-catalyzed amidation/dimerization of anilides via regioselective C(sp(2))-H functionalization is achieved. The para-selective amidation is accomplished on the anilide aromatic ring via a radical pathway leading to C-N bond formation in the presence of ammonium persulfate as a radical source/oxidant for the copper catalyst. The developed protocol tolerates a wide range of anilide substrates. The regioselectivity is confirmed by single-crystal X-ray studies.

}, issn = {1359-7345}, doi = {10.1039/c9cc09824k}, author = {Viveki, Amol B. and Garad, Dnyaneshwar N. and Gonnade, Rajesh G. and Mhaske, Santosh B.} } @article {46996, title = {Pd-iminocarboxylate complexes and their behavior in ethylene polymerization}, journal = {Chemistry-An Asian Journal}, volume = {15}, year = {2020}, month = {FEB }, pages = {398-405}, type = {Article}, abstract = {

Designing co-catalyst-free late transition metal complexes for ethylene polymerization is a challenging task at the interface of organometallic and polymer chemistry. Herein, a set of new, co-catalyst-free, single-component catalytic systems for ethylene polymerization have been unraveled. Treatment of anthranilic acid with various aldehydes produced four iminocarboxylate ligands (L1-L4) in very good to excellent yield (75-92 \%). The existence of 2-((2-methoxybenzylidene)amino) benzoic acid (L1) has been unambiguously demonstrated using NMR spectroscopy, MS and single-crystal X-ray diffraction. A neutral Pd-iminocarboxylate complex [{N O}PdMe(L1)] (N O=kappa(2)-N,O-ArCHNC6H4CO2 with Ar=2-MeOC6H4) C1 was prepared by treating stoichiometric amount of L1.Na with palladium precursor. The identity of C1 was confirmed by 1-2D NMR spectroscopy and single-crystal X-ray diffraction studies. Along the same lines, palladium complexes C2-C4 were prepared from ligands L2-L4 respectively. In-situ high-pressure NMR investigations revealed that these Pd complexes are amenable to ethylene insertion and undergo facile beta-H elimination to produce propylene. These palladium complexes were then evaluated in ethylene polymerization reaction and various reaction parameters were screened. When C1-C4 were exposed to ethylene pressures of 10-50 bar, formation of low-molecular-weight polyethylene was observed.

}, keywords = {imine, Imine-carboxylate, Insertion polymerization, Pd complexes, Polyethylene}, issn = {1861-4728}, doi = {10.1002/asia.201901501, Early Access Date = JAN 2020}, author = {Deshmukh, Satej S. and Gaikwad, Shahaji R. and Gonnade, Rajesh G. and Pandole, Satish P. and Chikkali, Samir H.} } @article {47378, title = {Polymorphs and hydrates of the anticancer drug erlotinib: X-ray crystallography, phase transition and biopharmaceutical studies}, journal = {CrystEngComm}, volume = {23}, year = {2021}, month = {JUN}, pages = {3961-3974}, type = {Article}, abstract = {

Erlotinib, a non-small cell lung cancer BCS class II drug, was found to occur as two polymorphs and two hydrates depending on the crystallization conditions. The monohydrate (form III), which has been reported in patents and publications, is the preferred crystalline phase from solution crystallization. The other forms (polymorphs, forms I and II, and a trihydrate, form IV) are solvent and condition-specific. Form I was exclusively and reproducibly obtained from dried non-polar solvents (viz. toluene, benzene, and xylene) using a solution crystallization method under controlled conditions. In contrast, form II was obtained by the rotary evaporation technique under reduced pressure from polar solvents (viz. dichloromethane, ethyl acetate, acetone, and acetonitrile). Slow evaporation from polar and non-polar solvents under open conditions yielded form III crystals, whereas evaporation from acetone-acetonitrile-water mixtures yielded form IV crystals. DSC and variable temperature PXRD studies revealed form I to be the most stable phase while the other solid forms displayed thermally induced polymorphic transitions into form I crystals. Further, form I and form III are found to be stable over the 30-90\% RH range. Further, form I displayed solution-mediated transformation into form III (monohydrate) when left to stand in the mother liquor for a longer duration (1-2 days). Similarly, the unstable form IV crystals transformed into the stable form III crystals within 1-2 h when exposed to an open atmosphere. Fast crystallization from polar solvents using the rotary evaporation technique enabled us to capture the metastable polymorph, form II. Early separation of form I from its mother liquor prevented its solution-mediated transformation into the monohydrate, form III. The water activity study revealed that form III is the most preferred solid phase in the presence of water. Dissolution rate measurements showed that the rate of form II is almost comparable to that of the marketed erlotinib hydrochloride. In contrast, for the other forms, the dissolution profiles showed a considerable decrease. Although the crystal structures of form I and form III have been published previously, this manuscript gives a comprehensive overview of the free base solid forms of erlotinib, the phase transitions amongst them and their biopharmaceutical properties.

}, doi = {10.1039/d1ce00032b, Early Access Date = APR 2021}, author = {Thorat, Shridhar H. and George, Christy P. and Shaligram, Parth S. and Suresha, P. R. and Gonnade, Rajesh G.} } @article {48124, title = {Polymorphs of green fluorescence protein chromophore analogue: fluorescence switching with thermal stimuli}, journal = {Crystal Growth \& Design}, volume = {22}, year = {2022}, month = {MAR }, pages = {1892-1905}, type = {Article}, abstract = {

Polymorphs of fluorescent organic materials offer significant implications in optoelectronics and advanced materials as they modulate photoluminescence properties. A slight alteration in the conformation/packing of molecules in the crystals shows variation in photoluminescence. This necessitates the polymorph screening of these materials to develop novel crystalline forms with distinct fluorescence emissions for broader application. In continuation of our work on the polymorph screening of Green Fluorescence Protein Chromophore (GFPc), we have synthesized a new imidazoline derivative, ethyl (Z)-2-(2-methyl-5-oxo-4-(3,4,5-trimethoxybenzylidene)-4,5-dihydro-1H-imi dazol-1- yl)acetate (1). Polymorph screening of 1 under different crystallization conditions revealed three polymorphs, Form I (needle), Form II (block), and Form III (polycrystalline material). Forms I and II are the outcome of solution crystallization, whereas Form III was produced from the melt crystallization of Forms I and II. DSC, HSM, and powder and single-crystal XRD studies indicate the conversion of Form I and Form III crystals to Form II crystals on thermal stimuli. The photoluminescence studies revealed cyan, yellow, and yellowish-green fluorescence emission for Forms I, II, and III crystals, respectively. The difference in photoluminescence could be due to the variance in aggregation modes like H-aggregation in Form I and J-aggregation in Form II crystals. Form I, Form II, and Form III crystals also showed irreversible thermal fluorescent switching from cyan-yellow-green due to polymorphic phase transitions. The study correlates the direct observation of the modulation of the excited-state transition under thermal stimuli in the crystalline phase. It will help augment the pace in the research of thermally responsive fluorescent materials.

}, issn = {1528-7483}, doi = {10.1021/acs.cgd.1c01459}, author = {Mali, Bhupendra P. and Dash, Soumya Ranjan and Biswas, Anupam and Vanka, Kumar and Manoj, Kochunnoonny and Gonnade, Rajesh G.} } @article {48270, title = {Palladium-catalyzed chemoselective oxygenation of C(sp2)-H and C(sp3)-H bonds in isatins}, journal = {Organic Letters}, volume = {25}, year = {2023}, month = {MAR}, pages = {1862-1867}, type = {Article}, abstract = {

The palladium-catalyzed chemoselective C(sp2)-H and C(sp3)-H bond oxygenation of substituted isatin derivatives is reported. This mild protocol exhibits the C5 C(sp2)-H oxygenation of isatins through electrophilic intermolecular C-H palladation in concentrated solutions using PhI(OAc)2 or Selectfluor as an oxidant, whereas it exhibits- N-CH3 C(sp3)-H oxygenation in dilute solutions via carbonyl-assisted intramolecular palladation in the presence of K2S2O8. This oxygenation reaction provides a direct and unified approach for synthesizing diverse oxygenated isatins with sensitive functionalities, including biorelevant compounds.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.3c00342}, author = {Vijaykumar, Muniyappa and Pradhan, Chandini and Gonnade, Rajesh G. and Punji, Benudhar} } @article {48671, title = {Palladium-catalyzed polar solvent empowered synthesis of hyper-branched ethylene oligomers and their applications}, journal = {Polymer Chemistry}, volume = {14}, year = {2023}, month = {JUL}, pages = {3239-3251}, type = {Article}, abstract = {

In this contribution, we report the synthesis of two naphthoxy imine ligands, 2-(((2,6-dibenzhydryl-4-methoxyphenyl)imino)methyl)naphthalen-1-ol (L1) and 2-(((2,6-diisopropylphenyl)imino)methyl)naphthalen-1-ol (L2), with different steric and electronic features. L1 and L2 were treated with [(TMEDA)PdMe2] to obtain the corresponding neutral palladium(ii) complexes Cat.1 and Cat.2 in excellent yields. The identity of Cat.1 and Cat.2 was unambiguously ascertained using a combination of spectroscopic and analytical methods, including single-crystal X-ray diffraction. When exposed to 5 bar ethylene pressure, Cat.1 produced hyperbranched ethylene oligomers. The microstructure analysis of ethylene oligomers confirmed the existence of methyl, ethyl, propyl, and sec-butyl branches, with a molecular weight (M-n) of 500-1400 g mol(-1), a PDI of 1.46-2.10, and 67-106 branches per 1000 carbon atoms. The use of a polar solvent, tetrahydrofuran, led to a remarkable 3-fold increase in oligomerization activity without compromising the branching and molecular weight. The resultant hyperbranched ethylene oligomers were selectively monofunctionalized using industrially practiced hydroformylation, ozonolysis, and epoxidation, almost quantitatively. The hydroxy functionalized ethylene oligomer (F4) (5 wt\%) was melt-compounded with LLDPE and Nylon-6 to produce a tough yet flexible blend with a higher strain-to-failure as compared to an uncompatibilized blend.

}, issn = {1759-9954}, doi = {10.1039/d3py00311f}, author = {Birajdar, Rajkumar S. and Gonnade, Rajesh G. and Pol, Harshawardhan V. and Prabhu, M. Basava and Rokade, Dhammaraj and Nandimath, Sheetal and Chikkali, Samir H.} } @article {48479, title = {Polymorph II of hydroxyurea 150 years after its first synthesis}, journal = {Crystengcomm}, volume = {25}, year = {2023}, month = {MAY}, pages = {2712-2716}, type = {Article}, abstract = {

A new polymorph of hydroxyurea (HU) was crystallized 150 years after its first synthesis. Due to its medicinal use in neoplastic diseases and sickle cell anemia, a high throughput screen of HU binary cocrystals was attempted. Instead of a cocrystal, an isoenergetic form II crystallized concomitantly with urea in methanol.

}, doi = {10.1039/d3ce00163f}, author = {Rai, Sunil K. and Tothadi, Srinu and Arhangelskis, Mihails and George, Christy P. and Gonnade, Rajesh G. and Nangia, Ashwini K.} }