A silver-catalyzed [3 + 3]-annulation cascade of alkynyl alcohols and α,β-unsaturated ketones for the regioselective assembly of chromanes

Abstract

An unprecedented Ag(I)-catalyzed [3+3]-annulation of alkynyl alcohols (5-hexyn-1-ols) and α,β-unsaturated ketones is reported to construct simple to complex chromanes. This transformation begins with hydroalkoxylation of alkynol through C-C triple bond...

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

“…While the precise reaction mechanism requires further investigation, plausible mechanistic pathways have been postulated based on results presented above and earlier studies conducted by our group [14][15][16] and others. 7a-d In this annulation, 5-hexyn-1ol (1) undergoes intramolecular hydroalkoxylation catalyzed by bismuth(III) triflate, leading to the generation of exocyclic enol ethers T1/T3.…”

“…13 In our ongoing exploration of alkynols chemistry (using as carbonyl surrogates), we've previously described [3+2] and [3+3] annulation reactions involving alkynols 1 and 2 with a-ketoesters Scheme 1 Our previous cascade annulation reactions involved alkynols and this work. 3 and enones 4, which facilitated the rapid synthesis of scaffolds like [5,5]-oxaspirolactones P1, 14 furo [2,3-b]pyran-2-ones P2, 15 chromanes P3, 16 and more 17 (entry A, Scheme 1). Building upon this work and motivated by the unique reactivity and biological potential of saccharin-derived N-sulfonyl ketimines, we now present a Bi(OTf) 3 -promoted [4+2]-annulation reaction of N-sulfonyl ketimines with 4-pentyn-1-ols 2 and 5-hexyn-1-ols 1.…”

“…Oxygen-inserted secondary alkynol 1e produced inseparable regio-isomers 6ej and 6ej’ . Known 16 optically pure butenolide-derived alkynol resulted in pentacyclic heterocycle 6fj as a single diastereomer (Scheme 2). 20…”