Preparations of 6-substituted 6H-Dibenzo[b,d]thiopyrans and their S-oxides through nucleophilic additions to 6H-dibenzo[b,d]thiopyran-6-one

Methods for the preparations of 6-substituted 6H-dibenzo[b,d]thiopyrans and the corresponding S-oxides were explored. The most general procedure involved the addition of Grignard reagents to 6H-dibenzo[b,d]thiopyran-6-one, whereupon 6-substituted 6H-dibenzo[b,d]thiopyran-6-ols were formed. The carbonyl group in the thioester thus behaved like an isolated ketone in its reactions with nucleophiles. The resultant dibenzothiopyran-6-ols were acid-labile, and dehydration products underwent further modification in some instances. Oxidation of the olefins afforded stable S-oxides. The dianion formed by reduction of dibenzothiophen also offered routes to 6-substituted 6Hdibenzo[b,d]thiopyrans, but the reactions of this dianion were non-regioselective and thus were of limited use.