Abstract
Reaction of 2-Diazopropane and 1,3-Thiazole-5(4H)-thiones. At O°, 1,3-thiazoles 1 and 2-diazopropane in pentane or MeOH undergo a smooth 1,3-dipolar cycloaddition to give spirocyclic 2,4-dihydro-1,3,4-thiadiazoles 6 (Scheme 3). Elimination of N2 occurs already at 20°, yielding spirocyclic thiiranes 7. At room temperature, the latter decompose slowly to give 4,5-dihydro-5-isopropylidene-1,3-thiazoles 8. The desulfurization 7 to 8 can be accelerated by heating or by addition of trimethyl phosphite. The intermediate of the N2 elimination of 6 is a thiocarbonyl ylide D which can be trapped with the reactive dipolarophiles thiobenzophenone and fumarodinitrile (Scheme 4). In the absence of these trapping reagents, D undergoes ring closure to thiiranes 7. The cycloaddition of D and a second molecule of 1, the so-called Schönberg reaction, is not observed.
Mlostoń, Grzegorz