Thermal Rearrangements of 3,3-Spiroalkylated Pyrazoles: Ring Expansion and Novel Cases of Sequential 1,5-Shifts
摘要:
A 3,3-spiro-(cyclopentyl)pyrazole containing electron withdrawing ester groups undergoes readily ring expansion in the form of the van Alphen-Huettel rearrangement. Subsequent post van Alphen-Huettel rearrangement involved a sequence of 1,5-shifts different from that suggested earlier. Reactive intermediates have been isolated and identified. The corresponding phenyl analog does not exhibit post van Alphen-Huettel rearrangement. A rationale for the different behavior is offered. X-Ray crystallography has been applied to differentiate between structurally similar product.