Six-membered Rings containing more than One Nitrogen

Six-membered Rings Containing More than One Nitrogen. - The tetrahydropyrimidones (229) are formed in excellent yields via a [4+2] cycloaddition of the 1,3-diazabutadienes (227) with diphenylketene (228),131 134 and mild base-catalysed isomerization of the 1,2-dialkylindazolones (230) gives the dihydroquinazolinones 

Barluenga et al. have reported the first example of a Diels-Alder reaction between an electronically neutral 

The product tetrahydrotriazines (235) are formed in excellent yields and under mild conditions. 

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