Applications of 1-Alkenyl-1,1-Heterobimetallics in the Stereoselective Synthesis of Cyclopropylboronate Esters, Trisubstituted Cyclopropanols and 2,3-Disubstituted Cyclobutanones

1-Alkenyl-1,1-heterobimetallics are potentially very useful in stereoselective organic synthesis but are relatively unexplored. Introduced herein is a practical application of 1-alkenyl-1,1-heterobimetallic intermediates in the synthesis of versatile cyclopropyl alcohol boronate esters, which are valuable building blocks. Thus, hydroboration of 1-alkynyl-1-boronate esters with dicyclohexylborane generates 1-alkenyl-1,1-diboro species. In situ transmetalation with dialkylzinc reagents furnishes 1-alkenyl-1,1-borozinc heterobimetallic intermediates. Addition of the more reactive Zn—C bond to aldehydes generates the key B(pin) substituted allylic alkoxide intermediates. An in situ alkoxide directed cyclopropanation proceeds with the formation of two more C—C bonds, affording cyclopropyl alcohol boronate esters with three new stereocenters in 58−89% isolated yields and excellent diastereoselectivities (>15:1 dr). Oxidation of the B—C bond provides trisubstituted α-hydroxycyclopropyl carbinols as single diaste...