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1,3‐Dipolar Cycloadditions of Ethyl 2‐Diazo‐3,3,3‐trifluoropropanoate to Alkynes and [1,5] Sigmatropic Rearrangements of the Resulting 3 H ‐Pyrazoles: Synthesis of Mono‐, Bis‐ and Tris(trifluoromethyl)‐Substituted Pyrazoles
Author(s) -
Gladow Daniel,
DonizKettenmann Sebastian,
Reissig HansUlrich
Publication year - 2014
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.201400032
Subject(s) - chemistry , phenylacetylene , sigmatropic reaction , diphenylacetylene , cycloaddition , diazo , medicinal chemistry , cyclopropene , ethyl diazoacetate , stereochemistry , organic chemistry , cyclopropanation , catalysis
The 1,3‐dipolar cycloadditions of ethyl 2‐diazo‐3,3,3‐trifluoropropanoate with electron‐rich and electron‐deficient alkynes, as well as the van Alphen Hüttel rearrangements of the resulting 3 H ‐pyrazoles were investigated. These reactions led to a series of CF 3 ‐substituted pyrazoles in good overall yields. Phenyl‐ and diphenylacetylene proved to be unreactive, but, at high temperature, the diazoalkane and phenylacetylene furnished a cyclopropene derivative. As expected, the 1,3‐dipolar cycloaddition to the ynamine occurred much faster than those to electron‐deficient alkynes. With one exception, all cycloadditions proceeded with excellent regioselectivities. The [1,5] sigmatropic rearrangement of the primary 3 H ‐pyrazoles provided products with shifted acyl groups; products resulting from the migration of a CF 3 group were not detected. In agreement with literature reports, this rearrangement occurs faster with 3 H ‐pyrazoles bearing electron‐withdrawing substituents.