@article {48955, title = {Regioselective synthesis of benzannulated [5,6]-oxaspirolactones via Cu(II)-catalyzed cycloisomerization of 2-(5-Hydroxyalkynyl)benzoates}, journal = {Journal of Organic Chemistry }, volume = {88}, year = {2023}, month = {NOV}, pages = {16915-16933}, type = {Article}, abstract = {

Spiroketals and oxaspirolactones are widely found in biologically active natural products, serving as important structural motifs. In this study, we present a Cu-(II)-catalyzed cascade cycloisomerization of 2-(5-hydroxyalkynyl)-benzoates, enabling the regioselective synthesis of benzannulated [5,6]-oxaspirolactones containing an isochromen-1-one moiety. This strategy offers a rapid and efficient approach to access a diverse array of benzannulated [5,6]-oxaspirolactones. The methodology presented here showcases a broad substrate scope, delivering good yields and scalability up to gram scale. The structures of the oxaspirolactones were unequivocally confirmed through single-crystal X-ray analysis and by analogy using H-1 and C-13-{H-1} NMR data.

}, keywords = {Construction, Isocumarins, Strategies}, issn = {0022-3263}, doi = {10.1021/acs.joc.3c01751}, author = {Thorat, Sagar S. and Shimpi, Sagar P. and Sambherao, Pooja I. and Krishna, Gamidi Rama and Kontham, Ravindar} } @article {48937, title = {Bi(OTf)3-promoted cascade annulation of hydroxy-pyranones and unsaturated γ-ketoesters for the construction of polycyclic bridged pyrano-furopyranones}, journal = {Organic and biomolecular chemistry}, volume = {22}, year = {2024}, month = {JAN }, pages = {496-500}, type = {Article}, abstract = {

An efficient protocol for constructing complex three dimensional polycyclic bridged chromano-furopyranones and pyrano-furopyranones (closely related to bioactive natural products) via bismuth(III)-catalyzed cascade annulation of hydroxy-pyranones and unsaturated gamma-ketoesters is presented. This process involves intermolecular Michael addition, intramolecular hemiketalization, lactonization, formation of one C-C bond and two C-O bonds, rings, and contiguous stereocenters.

}, keywords = {1 3-Dicarbonyl Compounds, alkynols, Coumarins, Fungus}, issn = {1477-0520}, doi = {10.1039/d3ob01862h}, author = {Rathod, Akshay B. and Borade, Balasaheb R. and Sambherao, Pooja I. and Kontham, Ravindar} } @article {49028, title = {Divergent access to polycyclic spiro- and fused-N,O-ketals through Bi(OTf)3-catalyzed [4+2]-annulation of cyclic N-sulfonyl ketimines and alkynols}, journal = {Chemical Communications}, volume = {60}, year = {2024}, month = {JAN}, pages = {1144-1147}, type = {Article}, abstract = {

Bismuth(iii) triflate-catalyzed [4+2]-annulation of cyclic N-sulfonyl ketimines (derived from saccharin) and alkynyl alcohols (4-pentyn-1-ols and 5-hexyn-1-ols) has been reported. This cascade annulation provides a diverse array of polycyclic spiro-and-fused N,O-ketals with excellent substrate scope, good isolated yields, and diastereoselectivities under mild reaction conditions.

}, issn = {1359-7345}, doi = {10.1039/d3cc05599j}, author = {Nakate, Ashwini K. and Kataria, Priyanka and Sambherao, Pooja I. and Krishna, Gamidi Rama and Kontham, Ravindar} }