The reactions of phthalazinium-2-(unsubstituted)methanide and aryl(3-phenylprop-2-en-1-ylidene)ammoniomethanide 1,3-dipoles with some thioester and thioketone CS dipolarophiles. Regio- and stereo-chemistry: substituted thiazolo-[4,3-a]- and -[2,3-a]-phthalazines and 2- and 4-styryl substituted tetrahydrothiazoles

Abstract

In cycloaddition reactions of phthalazinium-2-methanide and aryl(3-phenylprop-2-en-1-ylidene)ammoniomethanide 1,3-dipoles with thiobenzophenone, phenyl dithioacetate and methyl cyanodithioformate the regiochemistry was such that the nucleophilic methanide terminus of the dipole bonded to the sulfur atom, thus giving stereoisomeric substituted thiazolo[4,3-a]phthalazines and 4-styryl substituted tetrahydrothiazoles. With dicyclopropyl thioketone and thioadamantanone, steric effects caused a gradual reversal of this regiochemistry. Solvent polarity did not alter the distribution of regioisomers. X-Ray crystal structures are reported for 1,1-diphenyl[1,3]thiazolo[4,3-a]phthalazine 7 and 3-(p-bromophenyl)-4-[(E)-styryl]-5-trans-cyano-5-cis-methylthio-2,3,4,5-tetrahydrothiazole 15b.