New Avenues for the Synthesis of Oxa‐Cycles Using Lewis/Brønsted Acid mediated Carboxygenation and Carboalkoxylation of Alkynes

Abstract

The cascade functionalizations of alkynes have provided many elegant methods for the synthesis of useful scaffolds. Amongst these functionalizations, the ones comprising C‐C and C‐O bond formation have been utilized extensively due to the abundant presence of oxygenated motifs in various bio‐active natural as well as unnatural products. Transition‐metal catalysis is a mainstay for these tandem functionalizations as they are very efficient. However, their utilization does typically involve stoichiometric additives like other metal salts and/or Lewis acids/Brønsted acids (LA/BA). Thus, approaches that rely solely on using LA/BA, make these vital transformations not only eco‐friendly and atom economical but also cost beneficial are fast emerging as complementary alternatives. The present review addresses the gap in the literature by summarizing recent developments in LA/BA mediated 1,1/1,2‐carboxygenation and carboalkoxylation of alkynes for the synthesis of oxa‐cycles. The reaction mechanisms are particularly emphasized to bring out understanding needed from the point of future developments in this domain.