Adamantanethione and diazomethane; Dual regiochemistry of cycloadditions

Cycloadditions of diazoalkanes to thiones take place in two directions furn ishing 1,3,4-thiadiazolines and/or their 1,2,3-isomers, depending upon the substituents. Adamantanethione and diazomethane give rise to both regioisom ers; a literature report on the high solvent dependence of the isomer ratio is confirmed, and the two regioisomers are isolated. The 1,3,4-thiadiazoli ne 20 eliminates N-2 at 80 degrees C (t(1/2) 55 S) in a 1,3-dipolar cyclore version; the thiocarbonyl ylide 22 generated undergoes electrocyclization, forming a thiirane, or is intercepted by reactions with HX (thiols, alcohol s) or dipolarophilic multiple bonds. The N-2 extrusion from the isomeric 1, 2,3-thiadiazoline 21 is at 80 degrees C 600 times slower; the formation of the spirothiirane and homoadamantane-2-thione is explained by a diazonium t hiolate as an intermediate.