13C magnetic resonance studies. 120. The Simmons–Smith reaction with some silyl enol ethers. Unusual ring expansions of some norcamphorsti

Abstract

Unexpected difficulties with Simmons–Smith cyclopropanation of the trimethylsilyl enol ether of exo-tricyclo[3.2.1.02,4]-octan-6-one led to a reexamination of this reaction with the parent norcamphor derivative which under "concentrated" conditions gave ring-expanded allylic ethers in low yield. With the tert-butyldimethylsilyl ethers, however, the allylic product is formed in high yield in the norcamphor and exo-trimethylenenorcamphor (tricyclo[5.2.1.02,6]decan-8-one) systems. The tert-butyldimethylsilyl enol ethers of bicyclo[3.2.1]octan-6-one and nopinone do not undergo ring expansion under similar conditions but the silyl ether of 3-methylenenopinol is a major product in the latter case.