Abstract
AbstractDearomative cycloaddition of silylenes with diaryl ketones is an attractive chemical transformation to 5‐methylene‐1,3‐cyclohexadiene (o‐isotoluene) derivatives. We found that the dearomative (1+4) cycloadditions of an isolable dialkylsilylene (1) proceed faster with electron‐rich diaryl ketones and preferentially occur at an electron‐rich aromatic ring of unsymmetrically‐substituted diaryl ketones. Theoretical calculations indicated a carbonyl silaylide (a silylene‐ketone complex) is a key intermediate which is mainly stabilized by donor‐acceptor interactions of a lone pair orbital on oxygen atom of the diaryl ketones and a vacant 3p orbital of 1. The carbonyl silaylide undergoes the Si−C bond formation at the ortho‐position of one aryl ring to form a formal (1+4) cycloadduct with a very small activation barrier. Single crystal X‐ray crystallographic analysis of the (1+4) cycloadducts reveals their o‐isotoluene structures. UV‐vis absorption spectra of the (1+4) cycloadducts in hexane exhibit a π‐π* (HOMO‐LUMO) transition around 370 nm.
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