Thietes Subject

Meinwald and coworkers71 studied the chemistry of naphtho[l, 8-bc]thiete and its S-oxides. The reaction of the sulphone 2 with LAH (equation 29) is of particular and direct relevance to this section since it is different from the reductions that have been discussed thus far, because the major reaction pathway is now cleavage of an S—C bond, rather than a deoxygenation of the sulphur atom. The major product (equation 29) was isolated in 65% yield two minor products accounted for a further 15% yield. One of the minor products is 1-methylthionaphthalene and this was most probably produced by an initial reduction of the strained 1,8-naphthosulphone, 2, to the thiete, which was then cleaved to the thiol and subsequently methylated. Meinwald also showed71 that the thiete was subject to cleavage by LAH as well as that both molecules were susceptible to attack and cleavage by other nucleophiles, notably methyllithium. These reactions are in fact very useful in attempts to assess a probable mechanism for the reduction of sulphones by LAH and this will be discussed at the end of this section. 

Three isomers — 2//-naphtho[ 1,2-/dthiete 47, 1 //-2-naphtho[2,l -3]thiete 48, and 2//-1 -naphtho[2,3-7 ]thiete 49 -obtained in situ from 3-oxoH//-3,l-naphtho[l,2-z/]oxathiin, 3-oxo-l A/-4,2-naphtho[2,1 -z/]oxathiin, and 2-OXO-4//-3,1-naphtho[2,3-z/]oxathiin, respectively, were subjected to reaction with dimethyl or diethyl fumarate. Refluxing a solution of the corresponding precursors in toluene (for 49 in diethyl fumarate at 200 °C ) in the presence of... 

The photochemical reactions of thioketones have previously been the subject of a large number of papers, due mostly to Ohno, who pioneered this field, and to de Mayo. Current research involves more complete investigations of earlier work as well as the study of novel reactions. It has been confirmed that, on photochemical excitation, diaryl thioketones react in the ( ,w ) state with electron-rich olefins to give thietans or 1,4-dithians, and in the (ir,7r ) state with electron-deficient olefins to give thietans." Irradiation of aromatic thioketones at A > 540 nm with bis(methylthio)ethyne gives the previously unknown ajS-unsaturated dithio-esters (39), via the decomposition of an unstable thiet." ... 

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