Intramolecular Cyclopropanation of 1,4‐Dienes through Hydroboration–Homologation: Easy Access to Bicyclo[3.1.0]hexanes

Abstract

An intramolecular cyclopropanation reaction involving B-(1-chloroalkyl)catecholborane intermediates generated from 1,4-dienes through hydroboration with catecholborane and Matteson homologation was developed. This sequential procedure leading to bicyclo[3.1.0]hexanes involves the formation of three new sigma C-C bonds at the same carbon atom. A mechanistic study supports the involvement of carbocationic intermediates.

Intramolecular Asymmetric Cyclopropanation Using Air-Stable Alkylboronic Esters

“…formation. 27,[43][44][45][46][47] Remarkably, the diastereoselectivity of the cyclization step of 5′/13′ leading to B is the major factor determining the enantiomeric purity of the final products 6/14.…”

“…Some years ago, we reported a noncatalytic spontaneous intramolecular cyclopropanation process involving B -(1-chloro-5-alken-1-yl)catecholborane intermediates that were prepared through selective hydroboration of dienes and their subsequent Matteson homologation (Scheme 1 C). 27 Despite its efficacy, the utility of this process is hampered by the instability of the B -alkylcatecholborane (alkyl–Bcat) derivatives, which are notoriously air and moisture sensitive. Therefore, extending this reaction to air-stable pinacol boronic esters (R–Bpin) and related esters is highly desirable for practical reasons and for the development of an asymmetric version of this reaction.…”

“…In our initial work, 27 the B -(4-alken-1-yl)catecholboranes used for the Matteson homologation-cyclopropanation process were obtained by selective rhodium-catalyzed hydroboration of 1,4-dienes, but this proved to be challenging. An improved synthesis was developed and is presented in Scheme 2 .…”

“…[9][10][11] Methods based on highly reactive species such as carbenes and metallocarbenes have been applied for their preparation. [12][13][14] Approaches based on metallation of unsaturated terminal epoxides 15,16 and aziridines, 17 intramolecular Simmons-Smith cyclopropanation, 18 and sulfur ylide chemistry 19,20 have also been reported. Takai and Charette used pinacol dichloro-and diodomethylboronic esters in intermolecular cyclopropanation of alkenes leading to borylated cyclopropanes.…”

“…(16) Hodgson, D. M.; Chung, Y. K.; Nuzzo, I.; Freixas, G.; Kulikiewicz, K. K.; Cleator, E.; Paris, J.-M. J. Am.…”