Cyclopropyl building blocks of organic synthesis part 70 - 2-(bicyclopropylidenyl)- and 2-(trans-2 '-cyclopropylcyclopropyl)-4,4,5,5-tetramethyl-1,3-dioxa-2-borolane and their palladium-catalyzed cross-coupling reactions

摘要

The bicyclopropylidenylboronate 2 was prepared in 76% yield from lithiated bicyclopropylidene (1) and 2-isopropyloxy-4,4,5,5-tetramethyl- 1,3-dioxa-2-borolane. Birch reduction of 2 furnished 2-(trans-2'-cyclopropylcyclopropyl)-4,4,5,5-tetramethyl-1,3-dioxa-2-borola ne (3) in 79% yield. Under palladium catalysis, the latter was successfully coupled with a variety of aryl and alkenyl halides to give the corresponding (2'-cyclopropylcyclopropyl)-substituted arene 6 (52-75% yield) and alkene derivatives 11a,b (48-59%), respectively. Twofold and even threefold couplings of 2 with 1,2-dibromo- and 1,3,5-tribromobenzene were also successful. trans-3-(2'-Cyclopropylcyclopropyl)acrylic acid 12 could easily be obtained from 11a in 74% yield. [References: 31]