Synthesis of (Z)-alkenyl boronates via a copper(i)-catalyzed linear-selective alkylboration of terminal allenes

Abstract

A copper(I)-catalyzed intermolecular alkylboration of terminal allenes using unactivated alkyl iodides as the carbon electrophiles is reported. The regio- and stereochemistry of the product, (Z)-alkenyl boronate, could be constructed without the need to introduce directing groups. A wide range of terminal allenes substituted with prim-, sec- and tert-alkyl groups as well as heteroatoms are suitable for this reaction. Furthermore, the product can be used for the stereoselective synthesis of multi-substituted alkenes via Suzuki–Miyaura cross-coupling reactions. We also demonstrate the formal total synthesis of the marine natural product schizol A by means of the alkylboration of a terminal allene as the key step for the construction of the alkene moiety bearing two alkyl groups in a cis orientation. The direct precursor of schizol A was obtained with perfect stereoselectivity.