Novel Five/Five- and Six/Five-Membered Bicyclic Nitroso Acetals from High-Pressure-Promoted Cyclisation Reactions ofp-Methoxybenzyl Vinyl Ether, 1-Nitro-2-heteroaryl Ethenes, and Mono- and Di-Substituted Olefins

Abstract

At 15 kbar the 1-nitro-2-heteroarylethenes 2a−c reacted in a one-pot three-component cycloaddition with p-methoxybenzyl vinyl ether (1) and methyl acrylate to yield novel heteroaromatic-substituted six/five-membered bicyclic nitroso acetals. In the reaction of 3-[(E)-2-nitroeth-1-enyl]pyridine (2 equiv.) and 1 a competition between the formation of the tandem [4 + 2]/[3 + 2] cycloadducts and the formation of a novel five-membered cyclic nitronate was observed. The ratio of product formation was strongly pressure and solvent dependent. A mechanistic explanation for the formation of the novel five-membered cyclic nitronate has been proposed. 1-Nitro-4-[(E)-2-nitroeth-1-enyl]benzene (2d) reacted with 1 in the same manner as 2a in accordance with the proposed mechanism. The five-membered cyclic nitronate reacted as an 1,3-dipole in a high-pressure promoted [3 + 2] cycloaddition with both electron-rich and electron-poor olefins and yielded a novel class of pyridyl-substituted five/five-membered bicyclic nitroso acetals.