Enamines carbonyl group derivatization

Moreover, the carbonyl groups are represented in the numerous derivatives of carboxylic acids, namely amides, imides, and so forth. There are no derivatization methods for these compounds at present (excluding reduction), which are based on the reactions of the carbonyl group. Nevertheless, the amides react with (CH3)3SiCF3 in a manner similar to other carbonyl compounds. The hydrolysis of intermediate O-TMS derivatives followed by dehydration leads to the low boiling a-trifiuoromethyl enamines... 

The catalyst we will use Is the amino acid L-proline—no derivatization or protection required. It was actually back in 1971 that it was first noted that L-proline will catalyse asymmetric aldols, but until the year 2000 examples were limited to this one cyclization. Treatment of a triketone with proline leads to selective cyclization onto one of the two enantiotopic carbonyl groups. A molecule of proline must condense with the least hindered ketone, and in this case an enamine (rather than an iminium ion) can form. The chiral enamine can select to react with only one of the two other carbonyl groups, and it turns out that it chooses with rather high selectivity the one coloured green in the scheme below. Cyclization, in the manner of a Robinson annelation, and hydrolysis of the resulting iminium ion follow on, releasing the molecule of L-proline to start another catalytic cycle. The isolated product is the bicyclic ketone, in 93% ee. 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ ]

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