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Intramolecular Diels-Alder reaction of cyclenic trienes: Stereoselectivity and NMR structure determination
Blond, Alain,Platzer, Nicole,Guy, Alain,Dhotel, Helene,Serva, Laurence
, p. 283 - 293 (2007/10/03)
A series of trienes possessing an internally cyclenic dienophilic group undergo thermal intramolecular DielsAlder (IMDA) reaction with high selectivity for the cis-fused products. A concentrated solution of LIC1O4 in diethyl ether catalyzes the IMDA reaction of cyclenic nitrotrienes, giving rise to the irans-fused compounds. The stereochcmical outcome of these various processes are rationalized in terms of a minimization of the steric interactions between the ring and the chain on the one hand and the endo-stabilization from the nitro group on the other. The structures of the cycloadducts have been carefully determined by NMR 1H and 13C spectroscopy: dipolar interactions, detected via nuclear Overhauser effects, and criteria based on scalar coupling and moreover on chemical shifts have been employed. Conformational preferences were observed. Elsevier,.
