STEREO- AND REGIO-SELECTIVE ALDOL-TYPE REACTIONS OF ALKYLPYRIDINES WITH BENZALDEHYDE
作者:Hiroshi Hamana、Tsutomu Sugasawa
DOI:10.1246/cl.1984.1591
日期:1984.9.5
Stereo- and regio-selectivity in the reaction of alkylpyridines with benzaldehyde were studied. Erythro-selectivity could be obtained in the reaction of 2-alkylpyridine with benzaldehyde in the presence of dialkylboryl triflate and triethylamine. Substitution at the 2- or 4-position of 2,4-lutidine could be controlled by the combination of dialkylboryl triflate and an aliphatic tertiary amine. The steric effect had an important role in the reaction of 4-picoline and lepidine.
Selective Lithiation of 2-Methyloxazoles. Applications to Pivotal Bond Constructions in the Phorboxazole Nucleus
作者:David A. Evans、Victor J. Cee、Thomas E. Smith、Keith J. Santiago
DOI:10.1021/ol990027r
日期:1999.7.1
The lithiation of 2-methyloxazoles with alkyllithium and hindered lithium amide bases generally results in the competitive formation of a mixture of 5-lithio- and 2-(lithiomethyl)oxazole isomers. Herein a synthetically useful lithiation method which allows for the selective formation of 2-(lithiomethyl)oxazole is described. Diethylamine has been found to be a kinetically competent proton source that will mediate the equilibration of the kinetically formed 5-lithiooxazole to its more stable 2-(lithiomethyl)oxazole counterpart. Application of this metalation strategy with lithium diethylamide to two important bond constructions relevant to a projected phorboxazole synthesis is presented.