New thione chemistry

Abstract

Rate measurements reveal the superiority of C=S bonds over CC multiple bonds as dipolarophiles in cycloadditions of thiobenzophenone S-methylide, diphenyldiazomethane, and N-methyl-C-phenylnitrone. Thione S-oxides (sulfines) and thione S-sulfides likewise prefer thiones as cycloaddition partners. Many cycloadditions of thiones approach equilibria; the high reactivity is a kinetic phenomenon, the low HO-LU distance of the π-MOs being responsible. Ab initio calculations for H2C=S + H2C=NH+-O- result in a negative activation energy. π Bonds with silicon, phosphorus etc. exhibit likewise low HO-LU gaps and increased reactivity.