Activation of Alkynes with B(C_6F_5)_3 - Boron Allylation Reagents Derived from Propargyl Esters

摘要

Novel allyl boron compounds are readily synthesized via rearrangement reactions between Lewis acidic B(C_6F_5)_3 and propargyl esters. These reactions proceed through an initial cyclization followed by ring-opening and concurrent C_6F_5-group migration. In the absence of disubstitution adjacent to the ester oxygen atom, an allyl boron migration rearrangement leads to formal 1,3-carbobora-tion products. These allyl boron compounds act as allylation reagents with aldehydes introducing both a C_3-allyl fragment and a C_6F_5-unit as a single anti-diastereomer. In these reactions, B(C_6F_5)_3 activates the alkynes, prompting the rearrangement processes and enabling installations of C_6F_5 and R-groups.