Stereoselective Homocrotylation of Aldehydes: Enantioselective Synthesis of Allylic-Substituted Z/ E-Alkenes.

Cyclopropanated allyl- and crotylboron reagents participate in homoallylation and homocrotylation reactions that enable enantioselective access to motifs that otherwise require many steps to synthesize. In this study, we investigated the effect of substituents α- to boron, predicted either to counteract or reinforce the 1,3- selectivity of the parent reagents. We then investigated the transformation of the substituted homocrotylation products in intramolecular photocycloadditions to produce stereochemically complex natural-product-like scaffolds, finding that flow conditions enhanced the regioselectivity and yield.