摘要:
Dimethoxycarbene, generated from the norbornadienone ketal 6 or from triethyl orthoformate 12a can be trapped by various 1,2,4,5-tetrazines 1 to yield the corresponding isopyrazoles 10 in high yields via [4+1]-cycloaddition followed by [4+2]-cycloreversion. The less nucleophilic methoxy- or chlorophenylcarbenes react with the most activated tetrazine 1a only.