1.4- Dioxabutadienes

Hetero-l-oxabutadiene systems that have been shown to participate as 47t components of Diels-Alder reactions include vinylnitroso compounds (31, 2-aza-l-oxabutadiene, Chapter 9, Section 3), fV-acylimines (32) as well as aromatic and aliphatic acylisocyanates (33, X = O) and isothiocyanates (33, X = S, 3-aza-l-oxabutadiene, Chapter 9, Section 3), acylnitroso compounds (34,2-aza-l, 4-dioxabutadiene, Chapter 9, Section 3), selected 4-aza-l-oxabutadienes, e.g., 35, including o-quinone monoimines (36,... 

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