Formation of pyridin-4(1H)-one versus 1H-azepin-4(7H)-one by treatment of 4-tert-butyldimethylsilyloxy-2-amino-1-aza-bicyclo[4.1.0]hept-3-enes with tetrabutylammonium fluoride

Cycloadducts 3 and 4 were treated with tetrabutylammonium fluoride and rapidly suffer cleavage on the three-membered ring to form either pyridin-4(1H)-one or 1H-azepin-4(7H)-one. When R1 is an oxycarbonyl or a 2-pyridyl group and R2 is a negative charge-stabilizing group (cases 3a,b and 4f) the C-C bond cleaves forming products 5. However, when R2=H (case 3c) the ring expands to seven members. When R1 is an acyl group the pyridin-4(1H)-one formation includes an unexpected shift of the carbonyl group.