Convergence of Competitive Azidation, Elimination vs Substitution, and Preferential Ring Formation: Metal-Free,...

A series of polymesylated/polypropargylated polyols of different chain lengths were designed for the synthesis of the new varieties of 1,5-disubstituted 1,2,3-triazolyl fused bicyclic oxa-heterocycles under metal-free conditions. The orthogonally stable mesylated and propargylated polyol substrates were designed to avoid the use of highly reactive and/or unstable substrates decorated with azido and propargyl functionalities. The purpose was to allow the polymesylated/polypropargylated substrates to undergo intramolecular triazolylation under metal-free conditions to generate oxa-ring fused triazoles functionalized with azido or propargyl groups ready to undergo further transformation. These reactions were also expected to generate molecules constituted with two oxa-ring fused triazole units depending on the substrates. The reactions proceeded through the regioselectivity imposed by the nature of the azido group (primary or secondary), preference for the six-membered ring over the seven-membered ring, and/or the probability of competition between substitution and elimination reactions. All products confirmed the exclusive intramolecular triazolylation. Surprisingly, some of the substrates took an unprecedented and uncharted route in comparison to the predictable product formation of preformed monoazido-monoalkyne substrates affording olefinic products. The cyclization patterns of the azido-alkyne intermediates generated in situ from polymesylated/polypropargylated polyols were found to be substantially different from the preformed polyazido derivatives of propargylated polyols. Most of the 1,5-disubstituted 1,2,3-triazolyl fused bicyclic mono- and bis-heterocycles were reported for the first time. The importance of new functionalized fused triazoles as synthetic intermediates was established by preparing one linear polytriazole and two densely functionalized branched polytriazoles.