Trichloroacetyl-substituted derivative

The biomimetic total synthesis of (+)-20-epiervatamine was accomplished by J. Bosch et al. The authors used the addition of 2-acetylindole enolate to a 3-acylpyridinium salt as akey step to connect the two main fragments. The in situ formed 1,4-dihydropyridine was trapped with trichloroacetic anhydride to afford the corresponding trichloroacetyl-substituted 1,4-dihydropyridine derivative. The conversion of the trichloroacetyl group to a methyl ester was achieved by treatment with sodium methoxide. This transformation can be regarded as the second step of the haloform reaction. 

The C-acyl heterocycles do not generally form hydrates under acidic or alkaline conditions unless the five-membered ring is also substituted with a second electron-withdrawing group or, as with the trifluoroacetyl and trichloroacetyl derivatives, the carbonyl group is activated to nucleophilic attack. Such activated substituents also undergo the normal reactions with aqueous sodium hydroxide, sodium alkoxide and with amines to give the appropriate... 

The D-g/wco-pentitol-l-yl substituted uracil 96 and its D-galacto-isomer were synthesized from tri-O-benzyl-D-glucal and -o-galactal, respectively, by [2+2]cy-cloaddition of trichloroacetyl or chlorosulfonyl isocyanate, cleavage of the p-lactam rings in the products with methanol after AT-carbamoylation, and cycliza-tion of resulting glycosylureas. Tosylation of 4-(D-ga/acro-pentitol-l-yl)-2-phenyl-2/f-l,2,3-triazole led to the 3,6-anhydride 97 and two partially tosylated derivatives. ... 

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