Heterodienophiles, new, heterocyclic

Heterodienophiles, new, heterocyclic synthesis using, 55, 1 Heteropentalenes, 69, 271 Hilbert-Johnson reaction of 2,4-dialkoxypyrimidines with halogenoses, 8, 115... 

There have been reports on the reaction of oxazoles with heterodienophiles, including N=N, C=N, C=0, and types, to give new heterocycles <89X3535, 88JOO 663>. In most cases, the products may be envisioned to arise from ring opening and rearrangement of Diels-Alder adducts followed by reclosure, but so far no proof of this mechanism has appeared. A reaction of 5-ethoxy-... 

Bryce, M. R., Becher, J., Falt-Hansen, B., Heterocyclic Synthesis using new Heterodienophiles, 55, 1. 

The hetero-Diels-Alder reaction is amongst the most efficient processes for the synthesis of six-membered heterocyclic ring systems. Solvent-free conditions have been used to improve reactions of heterodienophiles and heterodynes with low reactivities. Cado et al. (1997) have described the hetero-Diels-Alder reaction of ethyl lH-perimidine-2-acetate as heterocyclic ketene aminal with ethyl propiolate nnder solvent-free conditions with focused microwave irradiation. The new fused perimi-dines (23) were obtained in good yields (67-98%). 

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