Pyrrolodiazines.: 5.: Synthesis, structure, and chemistry of pyrrolo[1,2-c]pyrimidine.: Dipolar cycloaddition of pyrrolo[1,2-c]pyrimidinium ylides

An improved synthesis of pyrrolo[1,2-c]pyrimidines, including the parent system, was accomplished via sequential condensation of substituted pyrrole-2-carboxaldehydes with tosylmethyl isocyanide (TOSMIC), followed by desulfonylation of the formed tosylpyrrolo[1,2-c]pyrimidines. Based on the ab initio calculations performed on the pyrrolo[1,2-c]pyrimidine 1a, some of the basic chemistry was investigated including electrophilic substitution, addition of organolithium reagents, metalation with lithium diisopropylamide (LDA) and subsequent reaction with electrophiles, and formation of salts by quaternization of the nonbridgehead nitrogen. Azomethine ylides generated from pyrrolo[1,2-c]pyrimidinium salts undergo 1,3-dipolar cycloaddition with suitable dipolarophiles to give new dipyrrolo[1,2-a;1',2'-c]pyrimidine derivatives, with high regio- and stereoselectivity.