Asymmetric Aldol Reaction of α‐Acetoxyimino Aldehydes and its Application in the Synthesis of Substituted 1,2‐Oxazine Derivatives

Abstract

Abstract:We have developed an asymmetric crossaldol reaction of a-acetoxyimino aldehydes with aldehyde pro-nucleophiles, catalyzed by proline, to afford g-acetoxyimino-b-hydroxy aldehydes in good yield with excellent enantioselectivity. The obtained aldol products have been successfully converted to 1,2-oxazines with four contiguous chiral centers in excellent diastereoselectivity in one-pot via sequential reactions such as deacetylation, oxy-Michael reaction and reduction.

Diaryl Prolinols in Stereoselective Catalysis and Synthesis: An Update

“…In the development of a diastereo‐ and enantioselective synthesis of γ‐acetoxyimino‐β‐hydroxy aldehydes, via L‐proline catalyzed cross‐aldol reaction of α‐acetoxyimino aldehydes, two examples promoted by diarylprolinol 1 b were reported by Hayashi et al . (Scheme ) …”

“…In the development of a diastereo-and enantioselective synthesis of γ-acetoxyimino-β-hydroxy aldehydes, via L-proline catalyzed cross-aldol reaction of α-acetoxyimino aldehydes, two examples promoted by diarylprolinol 1 b were reported by Hayashi et al (Scheme 9). [21] As usual, the aldol products were transformed into α,βunsaturated esters via Wittig reagent in toluene, to avoid the potential epimerization of the product. However, it was demonstrated that this precaution is unnecessary as the aldols, such as 9 a, could be isolated without observing epimerization.…”

Confirmation of the structure of (±)-preisomide by total synthesis

“…11 Grigg et al have reported that treatment of this aldehyde with hydroxylamine under mildly basic conditions yields nitrone 12 . 12 In contrast, inspired by a report by Yasui et al , 13 use of O -acetylhydroxylamine as its trifluoroacetate salt in the presence of excess potassium carbonate gave the desired dihydrooxazine 11 as the major product (33%) in a tandem condensation-intramolecular oxa-Michael addition, accompanied by some of nitrone 12 (17%). These compounds were easily separable by chromatography.…”