Mechanism of ring closure of aryl biguanide derivatives to isoammelines: Benzylation of dicyandiamide.

摘要

The literature provides conflicting evidence for the mechanism of ring closure accompanying the formation of s-triazines (s = symmetrical) from acyclic polyamine intermediates.{dollar}sp{lcub}(5,10,11,12,13){rcub}{dollar} This ambiguity provided our initial challenge which was to investigate the ring-closure mechanism as it applies to the formation of substituted 1-phenylammelines. Our first effort to unravel the complexity of these ring closures considered the addition reaction between phenyl isocyanate and phenylbiguanide. In this case where unsubstituted phenyl groups are involved the objective was to monitor the course of the reaction by means of a {dollar}beta{dollar}-emitting carbon-14 tag. For several reasons, our results from these experiments proved inconclusive. Owing to the lack of definitive results with the unsubstituted phenyl system we shifted our focus to systems which incorporated various substituents on the phenyl moieties. Therefore, a more manageable system was adopted which retained the symmetry of the proposed intermediate and allowed us to make use of the stable isotope label, deuterium. It was within these labeling experiments that two important discoveries were uncovered. The first has a significant impact on the composition of the final products, substituted phenylammelines, and the second provides a potential new thermal resist application based on a unique set of compounds. Both discoveries support one and the same ring-closure mechanism.; In addition to and complementary with our increased understanding of the cyclization mechanism, we had planned as an optimistic goal the synthesis of a multiprotected phenylbiguanide, which after condensation with phenyl isocyanate, would hopefully afford a stable acyclic structure. Subsequent deprotection of this material would under the right set of conditions yield the ammeline structure. The overall objectives were improved yields and a better "handle" for controlling the cyclization mechanism.; This synthetic approach was based on the utilization of the readily available, four-nitrogen building block, dicyandiamide (H{dollar}sb2{dollar}NC(=NH)NHCN, "dicy"). Although the final goal has not been realized we have been successful in making a significant contribution to the chemistry of dicy. Thus, for the first time a thorough study of the alkylation of dicy has been carried out and the electrophilic behavior of the nitrile group in two of these alkylated products has been explored.