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Diastereoselectivity and Reactivity in the Diels-Alder Reactions of α-Chloronitroso Ethers

✍ Scribed by Helena Felber; Günther Kresze; Roland Prewo; Andrea Vasella

Publisher
John Wiley and Sons
Year
1986
Tongue
German
Weight
631 KB
Volume
69
Category
Article
ISSN
0018-019X

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✦ Synopsis

The structure of the a-chloronitroso ether I, obtained from the hydroximolactone 2 and tert-butyl hypochlorite (89 %), was established by X-ray crystallographic analysis. The [4 + 2 1 cycloadditions of 1 with the dienes 3 and %I1 led to the N-unsubstituted 3,6-dihydro-2H-1,2-oxazines 6 and 12-16 in high enantiomeric excess (Table ). Due to the additional a-alkoxy group, the reactivity of 2 is much superior to the one of known a-chloronitrosoalkanes. The reactive conformation of 1 was deduced from the X-ray analysis as well as the high diastereoselectivity of the cycloadditions. The importance of the a-alkoxy group was evidenced from the similar reactivity of the racemic a-chloronitroso ethers 2 5 2 7 which were prepared from the hydroximo ethers 28-30 and tert-butyl hypochlorite.

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## Abstract The hetero Diels‐Alder reaction of the enamino ketones 1b and 1c with ethyl vinyl ether (2) in dichloromethane to give the dihydropyrans 3b/4b and 3c/4c is studied at high pressure up to 5 kbar. The kinetics is measured by on‐line FT‐IR spectroscopy up to 3 kbar. The cycloadditions show