engleski

Tandem Diels-Alder-aza-Michael reaction - a new synthetic approach to rigid polycyclic guanidines

Oxanorbornane is bicyclic structural motif present in a variety of biological systems [1] and it can be used as glycomimetics [2], β-turn inducers [3], amphiphilic systems for drug delivery [4], etc. Such structures can be prepared by a variety of methods the main being cycloaddition/hydrogenation sequence starting from substituted furans [1]. This synthetic approach has a high atom economy and both of these steps in combination with easily available furan derivatives from biomass could be considered eco-friendly. Herein, we report synthesis of a series of novel guanidine substituted oxanorbornanes by the cycloaddition/hydrogenation sequence. A special emphasis is laid on a tandem reaction encompassing cycloaddition/aza-Michael intramolecular addition what results in a formation of novel polycyclic guanidines. Efficiency of the intramolecular reaction is discussed in terms of the structural difference of the starting furfuryl guanidines 3a-3f. To rationalize the experimental results, pKa values as well as the reaction mechanisms were investigated by the DFT computational approach.

polycyclic guanidines ; oxanorbornanes ; cycloaddition

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