PYRROLODIAZINES .2. STRUCTURE AND CHEMISTRY OF PYRROLO[1,2-A]PYRAZINEAND 1,3-DIPOLAR CYCLOADDITION OF ITS AZOMETHINE YLIDES

A new synthesis of the pyrrolo[1,2-alpha]pyrazine system from pyrrole is described. In light of the ab initio calculations carried out on th is heterocyclic system some of its basic chemistry was investigated an d included electrophilic substitution, addition of organolithium reage nts, metalation with lithium diisopropylamide and subsequent reaction with electrophiles, and formation of salts by quaternization of the no nbridgehead nitrogen. N-ylides obtained from these salts undergo 1,3-d ipolar cycloaddition with suitable dipolarophiles to give dipyrrolo[1, 2-alpha]pyrazines, pyrazolo[1,5-alpha]-pyrrolo-[2,1-c]pyrazines, and h eterobetaines. Examples of intramolecular 1,3-dipolar cycloadditions a re also reported.