Fused Tetracyclic Heterocycles by Thermally Initiated Intramolecular Criss‐Cross Cycloaddition of 3‐Substituted Homoallenylaldazines

Abstract

Abstract The thermally initiated intramolecular criss‐cross cycloaddition of 3‐substituted homoallenylaldazines 5 has been explored. Their cyclization led to interesting new fused heterocyclic systems 6 consisting of four five‐membered rings with two nitrogen heteroatoms. The azines were prepared by the reaction of homoallenyl aldehydes 4 with hydrazine. The homoallenyl aldehydes 4 were synthesized by the Claisen rearrangement of new N , N ‐disubstituted 4‐[(2‐methylprop‐1‐en‐1‐yl)oxy]but‐2‐yn‐1‐amines 3a – f prepared by Mannich reaction of 2‐methylprop‐1‐en‐1‐yl prop‐2‐yn‐1‐yl ether ( 2 ). The success of the reaction was based on the improved solvent‐free synthesis of 1‐chloro‐2‐methylpropyl prop‐2‐yn‐1‐yl ether ( 1 ) and its conversion to isolable 2‐methylprop‐1‐en‐1‐yl prop‐2‐yn‐1‐yl ether ( 2 ) in high yield. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)