Activated carbodiimides, isocyanates, and isothiocyanates react with azanorbornenes, at room temperature, to give highly substituted, bicyclic guanidines, ureas, and thioureas respectively, in moderate to excellent yields via 1,3-diaza-Claisen rearrangements. The rearrangement is also observed upon reaction of azanorbornenes with unactivated isocyanates and isothiocyanates, at elevated temperatures. Competition experiments between isocyanates and isothiocyanates with limiting azanorbornene demonstrate that isothiocyanates react faster to afford rearrangement products. Given that isocyanates are more electrophilic, it is proposed that the reaction begins with a fast addition step followed by a rate-determining rearrangement step. Crossover experiments rule out the possibility that these bicyclic products are formed via a retro-Diels-Alder, [4+2]-cycloaddition process.
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