Atropisomeric Sulfur Reagents in Organic Synthesis: Diastereoselective Preparation and Reactions of 2-Benzoyldinaphtho[2,1-d:1′,2′-f] [1,3]dithiepine and Its S-Oxide

2 Benzoyldinaphtho[2,1-d:1′2′-f][1,3]dithiepine (4a) is reduced by lithium aluminum hydride to the alcohol 5a as a single diasteroisomer and reacts stereoseleclively with methylmagnesium iodide to give a 9:1 diastereoisomeric mixture of alcohols 6a. Dithiepine 4a was converted to its S-oxide 4b as a single diastereoisomer; in contrast, other open-chain analogs are formed as mixtures of diastereoisomers. Hydride reduction of 4b or its reaction with methylmagnesium iodide furnishes the alcohols 5b or 6b, respectively, as single diastereoisomers. The stereochemistry of the products was assigned via chemical and spectrscopic correlations with 5b′(obtained in the aldol reaction of the anion of the thiepine 3b with benzaldehyde), whose structure was unequivocally defined by an X-ray analysis.