Esters, from ketenes

Wiskur SL, Fu GC (2005) Catalytic asymmetric synthesis of esters from ketenes. J Am Chem Soc 127 6176-6177... 

Functional alkanes bearing a 2,3-dihydroxylated pattern are readily obtained, for example, aldehydes from l-acetoxy-2-alkenyl phenyl sulfones and esters from ketene acetals. ... 

Thiolic acid esters from ketene mercaptals... 

Thiolic acid esters from ketene mercaptals C C(SR)g > CHC(0)SR... 

In 2002, Fu et al. reported planar-chiral 4-(pyrrolidino)pyridine derivative (27) catalyzed enantioselective addition of amines with ketene to give acylpyroles with high ees (Scheme 2.68). They proposed the intervention of chiral Bronsted acid catalysis [129]. They employed (27) as a catalyst for the enantioselective synthesis of esters from ketenes [130]. 

An interesting bifunctional system with a combination of In(OTf)3 and benzoyl-quinine 65 was developed in p-lactam formation reaction from ketenes and an imino ester by Lectka [Eq. (13.40)]. High diastrereo- and enantioselectivity as well as high chemical yield were produced with the bifunctional catalysis. In the absence of the Lewis acid, polymerization of the acid chloride and imino ester occurred, and product yield was moderate. It was proposed that quinine activates ketenes (generated from acyl chloride in the presence of proton sponge) as a nucleophile to generate an enolate, while indium activates the imino ester, which favors the desired addition reaction (66) ... 

Ketene - [PSYCHOPHARMACOLOGICALAGENTS] (Vol20) -esters from pSTERIFICATION] (Vol 9)... 

Title Bioerodible Poly (Ortho Esters) from Dioxane-Based Di(Ketene Acetals) and Block Copolymers Containing Them... 

On the basis of these results, we have developed the first method for the enantiose-lective synthesis of chiral /3-amino acid esters from achiral imines and ketene silyl acetals using BLA 28. The enantioselectivity of the aldol-type reaction is dramatically increased by using sterically bulky A-substituents. Condensation of the imine derived from benzhydrylamine occurs with high enantioselectivity (90 % ee) (Eq. 80). Furthermore, the best result (96 % ee) is achieved by use of a 1 1 (v/v) mixture of toluene and dichloromethane as solvents. Thus, excellent enantioselectivity (95 % ee or better) has been achieved in reactions of aromatic aldehyde-derived imines... 

From ketene aminals, aminal esters and tris(dialkylamino)alkanes 577... 

For synthesis of arylacetic esters from aryl bromides and silyl ketene acetals, copper(II) fluoride is added to the reaction media besides the Pd catalyst."... 

Because of the higher priority give to sulfur, the Z monothioketene acetal derived from the corresponding monothioester is mechanistically equivalent to the ketene acetal derived from an ester. Care must be taken when comparing the results from monothioketene acetals with the results from ketene acetals to avoid confusion as a result of the nomenclature inversion. 

A new procedure for the preparation of P-trimethylsilyloxy ketones and esters from silyl enolates (128) and silyl ketene acetals (128a R = O ) has been developed by Yamamoto et al. (Scheme 54). Good to excellent yields of protected aldol products are obtained using a catalytic amount (O.OS-0.1 equiv.) of dimethylaluminum chloride. However, only a small degree of diastereoselectivity is obtained even when silyl enolates of high stereochemical purity are used. 

---