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Paper | Regular issue | Vol 55, No. 10, 2001, pp.1859-1871
Published online, 1st January, 1970
DOI: 10.3987/COM-01-9298
Thermal Rearrangements of 3,3-Spiroalkylated Pyrazoles: Ring Expansion and Novel Cases of Sequential 1,5-Shifts

Yao-pin Yen,* Shih-Feng Chen, Zan-Cheng Heng, Jen-Chieh Huang, Li-Chun Kao, Ching-Cheng Lai, and R. S. H. Liu

*Department of Applied Chemistry, Providence University, 200 Chungchi Road, Sha-Lu, Taichung Hsien, 433, Taiwan, R.O.C.


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.