First total synthesis of the antifungal antibiotic thiobutacin

Microwave-assisted synthesis of 4-oxo-2-butenoic acids by aldol-condensation of glyoxylic acid

“…With aliphatic substrates, these conditions yielded the desired products 3 and 12-17 with yields between 43% and 92%, in which no product was obtained with the TsOH-promoted conditions. In this case, substrates with additional enolisable centres were tolerated (3,(12)(13)(14)(15)(16)(17) and the internal aldol adduct was not observed. No desired product was obtained for the t-butyl ketone 18, presumably due to increased steric hindrance.…”

“…2). Literature reported conditions are typically acid-promoted, most commonly by acetic acid, 7,9-12 sulphuric acid, [13][14][15][16][17] phosphoric acid, 13,18 toluene-4-sulfonic acid 19 and formic acid, 20 with two acids frequently used together. 12,19,[21][22][23][24][25][26][27][28] The acid promotors are usually used neat or in large excess under reux for relatively long periods of time.…”