Bridgehead nitrogen heterocycles which contain the quinazoline moiety – synthesis and cycloaddition of 1,2-dihydroquinazoline 3-oxides

Organic & Biomolecular Chemistry Pub Date: 2005-11-16 DOI: 10.1039/B511998G

Abstract

A novel synthesis of 1,2-disubstituted 1,2-dihydroquinazoline 3-oxides 8 and the first ever examples of 1,3-dipolar trapping of these nitrones to homonuclear dipolarophiles is described. The new dipoles 8 reacted with N-methyl maleimide, generating diastereomeric adducts 14–16. In the reaction between 8 and dimethyl acetylenedicarboxylate, primary cycloadducts 17 and/or stable rearrangement products, azomethine ylides 18, are formed depending on the substitution pattern of the dipole. The structure of 18c is unambiguously assigned by X-ray crystallographic analysis. An X-ray crystal structure determination is also presented for the cyclopropylisoxazoloquinazoline 22 formed by a [3 + 2] addition of 8a to 21, the dimethyl acetylenedicarboxylate tetramer.

Graphical abstract: Bridgehead nitrogen heterocycles which contain the quinazoline moiety – synthesis and cycloaddition of 1,2-dihydroquinazoline 3-oxides
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