[Use of crystal conversion reactions in the synthesis of pentacyclic alkaloid analogues].
During investigation of substitution of debenzorutaecarpine derivatives thermal cyclization reactions was observed to produce new fused heterocyclic systems. The optimal temperature of cyclizations was determined by differential calorimetric measurements of crystals of intermediate products. The thermolysis of 2-azido-3-formil-debenzorutaecarpine gave, after elimination nitrogen, izooxazolo-debenzorutaecarpine in good yield. The cyclization of the 2-azido-3-nitroso-debenzorutaecarpine readily led to oxadiazolo E-ring analogue of rutaecarpine. The thermal cyclization of 2-hydroxy-debenzorutaecarpines gave 2-oxo- and 4-oxo-pyrano E-ring analogues of rutaecarpine. The structure of substances was confirmed by spectroscopic methods. The synthesised compounds are considered as first representatives of new heterocyclic ring systems.
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