Arylglyoxylates

Reactions.—Nucleophilic Attack at Carbon. (/) Carbonyls. Methyl arylglyoxylates react with trisdimethylaminophosphine (TDAP) to form m-a/S-dimethoxycarbonyl-stilbene oxides.63 The initially formed zwitterion (61) reacts with a second molecule of the ester to form a fra/ -diphenyl-1,4,2-dioxaphospholan intermediate, which undergoes a concerted symmetry-allowed retrograde n2s + 4 cycloaddition to give a carbonyl ylide, conrotatory cyclization of which leads to the cw-oxirans (62) (Scheme 3). 

Scheme 7.23 Stereoselective synthesis of bicyclic oxetanes in the PB reaction of arylglyoxylates.

Scheme 7.24 Stereoselective synthesis of oxetanes in the intramolecular PB reaction of arylglyoxylate derivative.

The photocycloaddition of methyl arylglyoxylates 90 with cyclo-1,3-dienes was investigated by Hu and Neckers (Sch. 26) [87]. These reactions proceed with high regioselectivity whereas the diastereoselectivity strongly depends on the nature of the aryl substituent. 

A simple access to 4-aryl-3-furanols is provided by the condensation of bis(alkoxycarbonylmethyl)ethers with various arylglyoxylates (Equation 35) <2001TL6429>. 

Simple extensions of this method involve the use of arylglyoxylic acids (e.g., phenylglyoxylic acid, PhCOCOjH) and a variety of pyruvic acids (RCH2COCO2H) and a-keto acids or their esters (Scheme 1). ... 

Hydrocarbon oxidation. A metal catalyst is usually required. By adding bis(/-riphenylsilyl) chromate," diphenylmethane is oxidized to benzophenone, and vanadium-pillared montmorillonite " catalyzes the conversion of arylacetic esters to arylglyoxylic esters by f-BuOOH. The presence of calcined ZnCrOj-hydrotalcite enables the selective generation of benzylic hydroperoxides from aralkanes."... 

Enantioface differentiating reduction of arylglyoxylic acids can be performed with NaBH4 in aqueous buffer media using a modified CD, 6-deoxy-6-amino-p-cyclodextrin [78]. The reaction proceeds with high yields but the arylglycolic acids obtained had low ee. The use of water-soluble chiral paracyclophanes does not increase the enantioselectivity of the reaction. 

The opposite behavior is evident in the Norrish type II photochemistry of arylglyoxylates that Neckers and co-workers have studied (Scheme The 1,4-biradicaI intermediate resulting from triplet-state... 

Hu, S. and Neckers, D.C., Photocycloaddition and ortho-hydrogen abstraction reactions of methyl arylglyoxylates structure dependent reactivities,/. Chem. Soc., Perkin Trans. 2, 1771,1999... 

---