Naphtho thiete, formation oxidation

Inasmuch as naphtho[l,8-Z c]thiete (34) was successively prepared by photolysis and thermolysis of naphthothiadiazine (42), Nakayama et al. (79JA7684) hoped to obtain in the same fashion naphtho[l,8-Z)c]thiete S-oxide (35) from naphtho[l,8-t/c]-1,2,3-thiadiazine S-oxide (50, Scheme 8). They attempted to synthesize sulfoxide 50 by oxidation of thiadiazine (42) with m-chloroperbenzoic acid (m-CPBA). However, this reaction carried out at room temperature with an equivalent amount of m-CPBA occurred with nitrogen liberation and with the formation of naphtho[l, 8-Z)c]thiete S-oxide (35) in 71% yield instead of the expected sulfoxide (50). 

The sulfur-sulfur interatomic distance in 9-phenyl-4,8,10-trithiadibenzo[cd,ij]a-zulene-8-oxide (417) is significantly shorter than the sum of their van der Waals radii and photolysis of (417) and (418) yields (420) and aldehydes or ketones (421) quantitatively. The unstable primary photoproduct (419) may be isolated and photolyses to (420) and (421). A similarly short sulfur-sulfur interatomic distance is found in a series of naphtho[l,8-ef][l,4]dithiepins and direct irradiation yields naphtho[l,8-cd][l,2]dithioles quantitatively with analogous S-S bond formation and alkene elimination. Photolysis of compounds (422), (424) and (426) gives the dimerised disulfides (423), (425) and (427) in 45%, 17% and 1% yields respectively. Irradiation of the tetraalkyl-2H-thietes (428) at 254 nm leads to a photostationary mixture containing the purple enethiones (429) (25%). Exposure of the mixture to 300 nm radiation induces almost complete reversion to (428). ... 

No evidence could be obtained for the formation of 2ff-benzo[i>]thiet or its valence tautomer by irradiation of 3/f-l, 2-benzodithiole l,l-dioxide. Naphtho-[l,8-6c]thiet (58) has been prepared and its 5-oxide, and S -dioxide, have been obtained by oxidation with m-chloroperoxybenzoic acid. All three compounds react with lithium aluminium hydride to give ring-opened products as the result of hydride attack on sulphur. After reduction and methylation, (58) gave the methyl sulphide (59), and the 5-oxide gave bis(a-naphthyl) disulphide (75%) together with (58) (6%) and the corresponding sulphone (4%), which was the major product (85%) from the 55-dioxide (Scheme 8). Thiets are believed to be... 

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