Reductive Metalation of 1,3-Diphenylisobenzofuran. Stereoselective Formation of Cis Products

Article abstract of DOI:10.1021/jo01308a006

1,3-Diphenylisobenzofuran was reduced in tetrahydrofuran by alkali metals to a dianion.This dianion on protonation, methylation, or carboxylation gave products which were predominantly cis.It is suggested that the dianion or the intermediate monoreacted monoanion adopts a preferred conformation in which steric interaction between the phenyl substituents is minimized and orbital overlap between the carbanion and the benzene ring is maximized.By use of this stereoselectivity of the dianion, a series of 1,3-polymethylene-bridged 1,3-diphenylphthalans was prepared.The possibility of single electron transfer during the alkylation of the dianion was examined by alkylating the dianion with tert-butyl halides.Complex reaction mixtures were formed but extensive alkylation occurred and mono- and dialkylation products were characterized.