@article {42448, title = {Efficient synthesis of gamma-keto sulfones by NHC-catalyzed intermolecular stetter reaction}, journal = {Organic Letters}, volume = {14}, year = {2012}, month = {MAY}, pages = {2830{\textendash}2833}, abstract = {

The N-heterocyclic carbene-catalyzed intermolecular Stetter reaction of aldehydes with α,β-unsaturated sulfones allows the atom-economic and selective formation of γ-keto sulfones in good yields. Key to the success of this unique transition-metal-free carbon{\textendash}carbon bond-forming reaction is the right choice of the NHC precursor and base. The reaction tolerates a broad range of different aldehydes.

}, doi = {10.1021/ol301045x}, author = {Bhunia, Anup and Yetra, Santhivardhana Reddy and Bhojgude, Sachin Suresh and Biju, Akkattu T.} } @article { ISI:000331163900009, title = {Efficient synthesis of 9-aryldihydrophenanthrenes by a cascade reaction involving arynes and styrenes}, journal = {Organic Letters}, volume = {16}, number = {3}, year = {2014}, month = {FEB}, pages = {676-679}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

A mild, general, and transition-metal-free protocol for the synthesis of 9,10-dihydrophenanthrenes is reported. The aryne generated by the fluoride-induced,1,2-elimination of 2-(trimethylsilyl)aryl triflates undergoes an efficient cascade reaction initiated by the Diels-Alder reaction with the differently substituted styrenes leading to the formation of 9-aryl-9,10-dihydrophenanthrene derivatives in moderate to good yields.

}, issn = {1523-7060}, doi = {10.1021/ol4033094}, author = {Bhojgude, Sachin Suresh and Bhunia, Anup and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {42444, title = {Employing arynes in transition-metal-free, N-heterocycles initiated multicomponent reactions}, journal = {Synlett}, volume = {25}, year = {2014}, month = {JAN}, pages = {608-614}, abstract = {

Transition-metal-free multicomponent reactions involving arynes, N-heterocycles, and various carbonyl compounds have been reported. With (iso)quinoline as the nucleophile and carbonyl compounds, such as aldehydes, ketones, and N-substituted isatins as electrophiles, the reaction afforded oxazino (iso)quinoline derivatives and the reaction proceeded via 1,4-dipolar intermediates. Interestingly, when the nucleophilic trigger used is pyridine, the reaction furnished indolin-2-one derivatives, and it is probable that the reaction proceeds via a pyridylidene intermediate.

}, keywords = {arynes - multicomponent reaction - oxindoles - pyridines - quinolines}, doi = {10.1055/s-0033-1340549}, author = {Bhunia, Anup and Biju, Akkattu T.} } @article {42425, title = {Employing arynes in diels{\textendash}alder reactions and transition-metal-free multicomponent coupling and arylation reactions}, journal = {Accounts of Chemical Research}, volume = {49}, year = {2016}, month = {SEP}, pages = {1658-1670}, abstract = {

Conspectus

Arynes are highly reactive intermediates having several applications in organic synthesis for the construction of various ortho-disubstituted arenes. Traditionally, arynes are generated in solution from haloarenes under strongly basic conditions. However, the scopes of many of the aryne reactions are limited because of the harsh conditions used for their generation. The renaissance of interest in aryne chemistry is mainly due to the mild conditions for their generation by the fluoride-induced 1,2-elimination of 2-(trimethylsilyl)aryl triflates. This Account is focused on the Diels{\textendash}Alder reaction of arynes and their transition-metal-free application in multicomponent couplings as well as arylation reactions.

The Diels{\textendash}Alder reaction of arynes is a powerful tool for constructing benzo-fused carbocycles and heterocycles. In 2012, we developed an efficient, broad-scope, and scalable Diels{\textendash}Alder reaction of pentafulvenes with arynes affording benzonorbornadiene derivatives. Subsequently, we accomplished the Diels{\textendash}Alder reaction of arynes with dienes such as 1,2-benzoquinones and tropones. Moreover, we uncovered a transition-metal-free protocol for the synthesis of 9,10-dihydrophenanthrenes by the reaction of arynes with styrenes that proceeds via a Diels{\textendash}Alder/ene-reaction cascade. In addition, we demonstrated the reaction of arynes with indene/benzofurans, which proceeds via a tandem [4 + 2]/[2 + 2] sequence.

Multicomponent coupling (MCC) involving arynes mainly comprises the initial addition of a nucleophile to the aryne followed by interception of the aryl anion intermediate with an electrophile (provided the nucleophilic and electrophilic moieties do not belong to the same molecule). We have disclosed aryne MCCs initiated by N-heterocycles such as (iso)quinoline, pyridine, and aziridines. When (iso)quinoline is used as the nucleophilic trigger and N-substituted isatin as the third component, the reaction affords spirooxazino(iso)quinolines via 1,4-dipolar intermediates. Unexpectedly, using pyridine affords indolin-2-ones, where the reaction proceeds via the pyridylidene intermediate. Additionally, we developed the phosphine-triggered aryne MCCs for the synthesis of functionalized benzooxaphospholes. In another phase of our work, we studied the synthetic utility of CO2\ as a one-carbon synthon in aryne MCCs for the synthesis of phthalimides.

Engaging arynes as an aryl source is one of the transition-metal-free methods for arylation reactions. We have demonstrated the N-arylation of aromatic tertiary amines and O-arylation of aliphatic alcohols using arynes.

It is anticipated that the chemistry of arynes will continue to prosper and will lead to surprising developments for the synthesis of various 1,2-disubstituted arenes of molecular complexity and structural diversity. Future challenges in this area include the utility of arynes in enantioselective transformations and the synthesis and reactions of exotic heterocyclic arynes.

}, keywords = {2-Benzoquinones; Cycloaddition, Facile N-arylation; O-arylation; One-Pot; Aldehydes; Benzyne; Amines; Heterocycles; Acids; 1}, doi = {10.1021/acs.accounts.6b00188}, author = {Bhojgude, Sachin Suresh and Bhunia, Anup and Biju, Akkattu T.} } @article {43351, title = {Enantioselective synthesis of spiro γ-butyrolactones by N-heterocyclic carbene (NHC)-catalyzed formal [3+2] annulation of enals with 3-hydroxy oxindoles}, journal = {Organic \& Biomolecular Chemistry }, volume = {16}, year = {2017}, month = {FEB}, pages = {2013 - 2019}, abstract = {The N-heterocyclic carbene (NHC)-catalyzed enantioselective formal [3 + 2] annulation of α,β-unsaturated aldehydes with 3-hydroxy oxindoles is presented. Under oxidative conditions using the bisquinone oxidant, the reaction resulted in the synthesis of spiro γ-butyrolactones in moderate to good yields, enantioselectivity and diastereoselectivity. The reaction likely proceeds via the generation of the NHC-bound α,β-unsaturated acylazolium intermediate from enals, which was intercepted by the dioxindoles in a formal [3 + 2] pathway to form the spirocyclic compounds. However, a deeper mechanistic investigation revealed that the reaction can also proceed via the homoenolate intermediate. In this case, the dioxindole was oxidized to the corresponding isatin derivative using traces of air under basic conditions, and was intercepted with the NHC-bound homoenolate intermediate in a formal [3 + 2] pathway to afford the spiro compound.}, doi = {10.1039/C7OB00148G}, author = {Mukherjee, Subrata and Joseph, Sumi and Bhunia, Anup and Gonnade, Rajesh Ghanshyam and Reddy, Santhi Vardhan and Biju, Akkattu T.} } @article {45358, title = {Employing arynes for the generation of aryl anion equivalents and subsequent reaction with aldehydes}, journal = {Journal of Organic Chemistry}, volume = {83}, year = {2018}, month = {SEP}, pages = {11333-11340}, type = {Article}, abstract = {

Arynes are highly reactive intermediates, which are utilized for the electrophilic arylation of various X-H bonds (X = O, N, S etc.). Herein, a new synthetic strategy is demonstrated, where arynes are converted into aryl anion equivalents by treatment with phosphines and a base. The addition of phosphines to arynes form the phosphonium salts, which in the presence of a carbonate base generates the aryl anion equivalent. Subsequent addition of the aryl anions with aldehydes afforded the secondary alcohols.

}, doi = {10.1021/acs.joc.8b01549}, author = {Gaykar, Rahul N. and Bhunia, Anup and Biju, Akkattu T.} }