Enantioselective Allylation of Selected ortho-Substituted Benzaldehydes: A Comparative Study

We report a systematic study of the allylation of ortho-substituted benzaldehydes under catalysis of a Lewis base (N, N-dioxide), a Lewis acid (Keck allylation), and a Bronsted acid. ortho-Halobenzaldehydes were used as the aldehydic substrates, and special attention was paid to ortho-vinyl and alkynyl benzaldehydes, which might serve as interesting synthons for the preparation of more complex chiral compounds. Similar enantioselectivities were achieved under catalytic conditions. In the case of ortho-halobenzaldehydes, Lewis base catalysis proved to be more efficient, and the highest asymmetric induction for allylation of ortho-fluorobenzaldehyde reached 82% ee, which is comparable to other used catalytic conditions. In cases of ortho-vinylbenzaldehyde, the Keck allylation provided the product in 88% ee. An enantioenriched homoallylic alcohol was used as the starting material for the synthesis of a sertraline intermediate.