Glyoxylic oxime ether

Indium-mediated allylation reactions of a-keto imides derived from Oppolzer s sultam proceeded in aqueous THF in good yields and excellent diastereoselectivity (Eq. 11.43).74 The indium-mediated allylation of the Oppolzer camphorsultam derivatives of glyoxylic oxime ether... 

Reaction with Propargyl Halides. The indium-mediated coupling of propargyl bromide with a variety of imines and imine oxides afforded homo-propargylamine derivatives in aqueous media under mild conditions.78 Propargylation of glyoxylic oxime ether in the presence of a catalytic amount of palladium(O) complex and indium(I) iodide in aqueous media was also studied (Eq.11.47).79... 

Allylboronates of type 103 react with equivalent amounts of aldoximes 102 (equation 73) giving allylhydroxylamines 104 in good yields. Similar reactions of aldoximes and glyoxylate oxime ethers with allyl bromide and indium also provide hydroxylamines. Additions of substituted allyl boronates to oximes produce mixtures of stereoisomers with ratio highly dependent on the steric size of substituents in both molecules. Addition of allyltri-n-butyltin to aldoxime ether 105 (equation 74) was found to proceed with a considerable diastereoselectivity. 

A subsequent similar synthesis of a-amino acids was then reported by Naito et al. which used the indium-mediated alkylation and allyation reaction of the Oppolzer camphorsultam derivative of glyoxylic oxime ether <02CC1454>. 

Allylation of electron-deficient imines with allylic acetates and Ini proceeds in the presence of a catalytic amount of Pd(0). The reversibility of allylation has been observed in the reaction of glyoxylic oxime ether bearing a camphorsultam moiety (Scheme 81). As an important effect of water on regioselectivity, the branched adducts are kinetically formed from mono-substituted allylic reagents in the presence of water. On the contrary, a selective formation of the thermodynamically stable linear adducts is observed in anhydrous THF.305,306... 

Naito and co-workers investigated aqueous medium radical addition to glyoxylic oxime ether due to its good reactivity in organic solvents.9 Its noteworthy that triethylborane acts as a radical initiator and terminator to trap the intermediate alkyl radical (Scheme 7.6). 

Jang and co-workers reported on the development of an enantioselective radical addition reaction to glyoxylate oxime ether for the preparation of a-amino acids under mild reaction conditions with chiral quaternary ammonium salts of hypophosphorous acid in aqueous media.26 The newly prepared chiral quaternary ammonium hypophosphites are inexpensive, less toxic than metal-containing compounds and the reaction conditions and workup are mild and simple (Table 7.2). It is also important to note that chiral quaternary hypo-phosphites are recyclable without altering their performance. The... 

Table 7.2 Radical addition reactions to glyoxylic oxime ether under various reaction conditions.

Scheme 20. Naito s radical addition to glyoxylic oxime ether...

Diastereoselective radical additions to glyoxylic oxime ethers are well established however, only one recent report describes attempted enantioselective additions using chiral Lewis acids [26], It was found that bisoxazoline ligand 9 provided the best results as illustrated in Eq. (18) and Table 3. 

A related application is the sysnthesis of a-substituted a-amino esters by addition of the intermediate alkyl radicals to glyoxylic oxime ethers. ... 

Scherrmann used a radical coupling between glyoxylic oxime ethers and p-C-glycosyl 2-iodopropane easily obtained from the corresponding p-C-glycosylpropan-2-one, giving access to C-glycosylthreonine and allothreonine. ... 

Scheme 15 Diastereoselective allylation of glyoxylic oxime ethers...

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