A new route to 1,5-disubstituted 4-arylsulfonylpyrazoles by lithiation of 1-methyl-4-arylsulfonylpyrazoles
作者:Michael G. Hoffmann
DOI:10.1016/0040-4020(95)00540-o
日期:1995.8
The arylsulfonylvinamidinium salts 1 reacted with hydrazine in refluxing ethanol to give rise to 4-arylsulfonylpyrazoles 2 in reasonable yield. Regioselective lithiation of N-methylpyrazoles 3 with LDA followed by treatment with various electrophiles afforded the corresponding 1,5-disubstituted 4-arylsulfonylpyrazoles 5 in good yield.
Dipolar cycloaddition reaction of diazoalkanes with trimethylsilyl substituted alkynes. Steric control of regiochemistry by the trimethylsilyl group
作者:Albert Padwa、M. Woods Wannamaker
DOI:10.1016/s0040-4020(01)86680-1
日期:1990.1
coefficient with that of the larger dipolarophile LU coefficient. Dipolar cycloaddition of several 2-(trimethylsilyl) substituted alkynes led to the unexpected regioisomer. Regiochemical control can be attributed to steric rather than to stereoelectronic factors when a bulky trimethylsilyl group is attached to the dipolarophile. In certain cases some of the cycloadducts undergo rearrangement to pyrazoles