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26.5.14.1.4 Method 4: From 1,2-Diketones or α-Oxoaldehydes

DOI: 10.1055/sos-SD-026-00616

Parrain, J.-L.; Thibonnet, J.Science of Synthesis, (200526854.

The reaction of 1,2-diketones with various primary heteroaromatic amines, including pyridine, diazine, and azole derivatives, has also been studied in order to prepare numerous oxo aminals. For example, the dione 378 reacts with 2-aminopyridine to give, in good yield, the propanone 379 as a stable product (Scheme 150).[‌572‌] It should be noted that with other amino heterocycles, only N-heteroaryl-α-imino ketones are obtained. Similarly, a dihydroquinazolinone is obtained from anthranilamide and benzil.[‌573‌] Amino amides 380 can also be used as a diamino source and react as trinucleophiles with vinyl vicinal tricarbonyl esters, e.g. 279 (Scheme 151). Reaction of the primary amino groups takes place at the β-position of the α,β-unsaturated ketone, along with addition to the central carbonyl group. In a third-stage reaction, the amide residue adds to the iminium ion formed from the intermediate carbinolamine (Scheme 151).[‌574‌,‌575‌] The resulting products, bicyclic or tricyclic (acylamino)pyrrolidonecarboxylates 381, are obtained in fair to good yield, considering the numbers of steps in the reaction. Novel tricyclic 3-azadethiacephams of biological interest have been prepared using this reaction.[‌576‌] Generally, the condensation of α-oxoaldehydes with aliphatic amines gives monoimines in nearly quantitative yield. Nevertheless, the course of the direct condensation of α-oxoaldehydes with anilines depends on the substitution. Mainly, electron-donating groups give the corresponding imines, whereas electron-withdrawing groups lead to the oxo aminals.[‌577‌,‌578‌] The reaction of alkoxypropenals 382 with diverse primary amides gives 3967% yields of the oxo aminals 383 (Scheme 152).[‌579‌] Finally, α-hydroxy aldehydes and their benzyl ethers are prepared by Grignard reactions of aminal 384 derived from (S)-2-(anilinomethyl)pyrrolidine and phenylglyoxal. For example, the aminal was treated with methylmagnesium iodide to give, after hydrolysis, 67% of (S)-(+)-2-hydroxy-2-phenylpropanal, in 95% ee.[‌555‌,‌557‌,‌580‌]

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