Hetero-Diels-Alder Cycloadditions of α,β-Unsaturated Acyl Cyanides, Part 4 , Substituent Effects in Reactions with p-Substituted Styrenes
✍ Scribed by Jin-Cong Zhuo; Hugo Wyler
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- German
- Weight
- 153 KB
- Volume
- 82
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Cycloadditions of a,b-unsaturated acyl cyanides ( 2-oxonitriles) 1 ± 6 to styrene and its p-substituted derivatives 7a ± f,h are of inverse electron demand and provide, under mild conditions, regio-and stereoselectively 2-aryl-3,4-dihydro-2H-pyran-6-carbonitriles 8 ± 13, generally in good yield. Rates for the cycloaddition of acryloyl cyanide 1 to p-substituted styrenes, determined in competition reactions of substrate pairs relative to that of styrene, increase in the order of electron-donating ability NO 2 Cl H AcO Me ÀcNH `MeO of the p-substituent. Linear correlation of log (k X /k H ), and s p substituent constants (a Hammett-type plot), gives a reaction constant 1 p of À 1.47 AE 0.17, supporting a concerted mechanism.
a ) Conditions A: 9 mmol of 1 in 30 ml of MeCN, and 5 mmol of styrene. b ) Conditions B: 5 mmol of 2 ± 6, and 5 mmol of styrene, neat.