Acetylation of benzoin

The only method of preparative interest is the acetylation of benzoin, either with acetyl chloride 1 or with acetic anhydride.2 The melting point of acetyl benzoin was reported by Zinin as below roo°, by Jena and Limpricht as 75° but by later investigators as 82-83°. 

Based on the known photoreduction chemistry of Rose Bengal [275], one would anticipate that electron transfer would reduce the xanthene skeleton of RBAX and that the radical anion thence formed might decay by the elimination of an acetyl radical. Acetyl is totally analogous to benzoyl, the radical that initiates chains in the case of most Norrish type I UV photoinitiators, that is, benzoin ethers or acetophenone acetals. The putative scheme is shown in Scheme 7. 

This reaction, similar in nature to the benzoin condensation, led to analogs of ascorbic acid. It was observed that the reaction proceeded especially well when a methyl alcoholic solution containing an acetylated sugar cyanohydrin and ethyl glyoxylate was treated with alkali. 

The asymmetric intramolecular crossed benzoin reaction catalysed by a chiral triazolium salt has been used to synthesise 3-hydroxychroman-4-ones 34 in good to high yields and ee. The absolute configuration at the quaternary stereocentre C-3 has been shown to be S by X-ray analysis of the camphanyl ester <06SL2431>. Both enantiomers of 2-(2-phenylethyl)chroman-4-one, flindersiachromanone, have been obtained from racemic l-phenylhex-5-en-3-ol after resolution via lipase-catalysed acetylation <06H(68)483>. 

JOC3221). Nitration of 6-methyl-[l,2,4]triazolo[3,4-a]phthalazine in fuming nitric acidconcentrated sulfuric acid produced the 8-nitro compound (190). On the other hand, attempted nitration of (17) with copper nitrate-acetic anhydride gave only the 3-acetyl compound. The Vilsmeier formylation failed on (17) (69JOC3221) however, deuterium exchange occurred at C-3. The 3-carbaldehyde (see synthesis section) underwent the benzoin condensation and was oxidized to the 3-carboxylic acid. 

His6-tagged protdns synthesis of (R)-benzoin, (R)-2-hydroxy-1-phenylpropan-l-one, and 6-O-acetyl-D-glucal in a flow-through mode... 

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