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3,5‐Disubstituted‐1,2,4‐oxadiazoles and 4,5‐dihydro‐3,5‐disubstituted‐1,2,4‐oxadiazoles
Author(s) -
Yale Harry L.,
Spitzmiller E. R.
Publication year - 1978
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570150825
Subject(s) - chemistry , diborane , annulation , regioselectivity , acetaldehyde , organic chemistry , medicinal chemistry , chloride , boron , catalysis , ethanol
A series of 3,5‐disubstituted‐1,2,4‐oxadiazoles ( 2 ) were prepared from a mono‐ or dichlorophenyl‐substituted amidoxime and (i) an acid chloride, (ii) an isatoic anhydride, or (iii) a β‐keto ester. Although cyclizations of the same amidoximes with acetaldehyde gave 4,5‐dihydro‐5‐methyl‐substituted derivatives ( 5 ), that annulation procedure either failed or gave low yields with other aldehydes. A novel alternative method, the diborane reduction of 2 , has been found to be a generally applicable procedure for preparing 5 . The reduction is regioselective, i.e. , only the 4,5‐(C=N) linkage is reduced even when a large excess of diborane is present.