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 sy stem, was accomplished via sequential condensation of substituted pyrrole-2 -carboxaldehydes with tosylmethyl isocyanide (TOSMIC), followed by desulfon ylation of the formed tosylpyrrolo[1,2-c]pyrimidines. Based on the ab initi o calculations performed on the pyrrolo[1,2-c]pyrimidine 1a, some of the ba sic chemistry was investigated including electrophilic substitution, additi on of organolithium reagents, metalation with lithium diisopropylamide (LDA ) and subsequent reaction with electrophiles, and formation of salts by qua ternization of the nonbridgehead nitrogen. Azomethine ylides generated from pyrrolo[1,2-c]pyrimidinium salts undergo 1,3-dipolar cycloaddition with su itable dipolarophiles to give new dipyrrolo[1,2-a;1',2'-c]pyrimidine deriva tives, with high regio- and stereoselectivity.