The preparation of polysubstituted bicyclo[3.1.0]hexanes starting from air-stable
substituted pent-4-en-1-ylboronic acid esters has been investigated. The method involves
a Matteson homologation with LiCHCl2, leading to 1-chlorohex-5-en-1-ylboronic acid ester intermediates. The subsequent
intramolecular cyclopropanation step was performed in a one-pot process. With pinacol
boronic esters, the cyclopropanation step was either performed thermally at 140 °C
or at 70 °C after in situ transesterification to form a catechol boronic ester. This
last approach is suitable for the preparation of enantioenriched bicyclo[3.1.0]hexanes
using either chiral-auxiliary control or by taking advantage of the sparteine-controlled
enantioselective boroalkylation of alcohols.
Key words
cyclopropanation - boronic esters - Matteson homologation - chloroalkylboronates -
bicyclo[3.1.0]hexanes - fused cyclopropanes