Adamantanethione 5-oxide cycloaddition

High-level quantum-chemical calculations on the 3 + 2-cycloadditions of thioformaldehyde 5 -imides, S -methylide, S-oxide, and 5-sulfide have been reviewed. Theoretical studies on the 1,3-dipolar cycloaddition between thioketene 5-oxide and methyleneimine show that this reaction is concerted but non-synchronous. Adamantanethione 5-methylide reacts with thiocarbonyl compounds to produce 1,3-dithiolanes. A density-functional-theory study of the cycloaddition of the sulfine H2CSO predicts the 2 + 3-mechanism having the lowest pathway, with an activation barrier of 12.3kcalmoP. R The thermal and photochemical reactions of fluorenethione 5-oxide (69) with cyclooctyne (70) involves an initial 1,3-dipolar cycloaddition to produce the adduct (71), followed by an efficient sulfur transfer to cyclooctyne to produce the enone (72) and the dithiin (73) (Scheme 26). ° ... 

Alkene Synthesis.—The alkene synthesis by two-fold extrusion processes (see Vol. 3, pp. 246, 693) is discussed in Chapter 2 of this Volume (p. 89). The addition of diazo-compounds to suitable thiones provides an alternative route to A -l,3,4-thiadiazolines, which give episulphides on pyrolysis and hence alkenes on further reaction with triphenylphosphine. The symmetrical 1,3,4-thia-diazoline represents the normal direction of cycloaddition, but the orientation of addition of diazomethane to adamantanethione is governed by the nature of the solvent, and the unsymmetrical adduct predominates in solvents of higher polarity. A -l,3,4-Thiadiazoline-2,5-dione (148) is generated by oxidation of... 

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