A new synthesis of phthalides by internal trapping in ortho-lithiated carbamates derived from benzylic alcohols
摘要:
The addition of t-BuLi to a low-temperature THF solution of o-bromocarbamates 2 leads to ortho-lithiated intermediates 3, in which internal trapping by the electrophile on the side chain then takes place. This novel Parham-type anionic cyclization procedure affords the variously substituted phthalides 5 in high yields and can also be used for the preparation of lactones 8, which are useful for the synthesis of aristocularine alkaloids.