Methyl glyoxylate, formation

Another enantiosdective variant of this reaction has been developed with a bi-nol-titanium complex 66 [46]. This catalyst affords homoallylic alcohols in moderate diastereo- and enantioselectivity with 2-butenylsilane ( )-16 and methyl glyoxylate (Scheme 10-25). Reaction of (Z)-16 was much less selective, providing homoallylic alcohols with low enantioselectivity. An antiperiplanar transition structure accounts for the formation of the syn homoallylic alcohol 67. A more reactive complex formed from BINOL and TiF4 has also found utility [46cj. 

A similar route has been suggested to account for the formation of glyoxylic acid (18, R = H) and methyl glyoxylate (18, R = Me) during the periodate oxidation of inositols and (9-methylinositols, respectively. Formation of these carboxy derivatives was depicted by sequences involving enolization to such reductones as 16, which are hydroxylated to 17 and then cleaved oxidatively. 

Gmha is an equilibrium mixture, which also contains some hydrated methyl glyoxylate. NMR ejqjeriments indicated that the formation peroxyhydrate from gmha and aqueous H2O2 is established slowly. 

Whitesell and Minton have synthesized (- )-xylomollin (408), the only trans-fiised iridoid, from the racemic bicyclic diene 409. Control of the stereochemistry was effected in the first step by addition of the glyoxylate 410. The two products were separated and the major one, 411, was reduced with lithium aluminum hydride. Conversion of the primary alcohol to a methyl group, with concomitant inversion of stereochemistry at the secondary alcohol carbon atom was carried out by protection of the primary alcohol function (fert-butyldimethylsilyl), tosylation of the secondary hydroxyl, then removal of the silyl group with formation of an epoxide with inversion, and reduction (LiEtaBH) of the epoxide. The remaining steps are shown in Scheme 36. It remains to point out that isoxylomoUin (412) was produced preferentially, and is indeed formed from xylomollin (408) slowly in methanolic solution. ... 

Urea, methylurea, and dimethylureas react with glyoxylic acid and its methyl ester to give a-substituted hydantoic acid derivatives (16) and substituted allantoic acid derivatives (17), which can be cyclized to 5-substituted hydantoins (18). Although allantoin (18) formation from urea and... 

Prompted by the use of oxalate and other additives and hy the observation of ds-diol formation in the hetereogenized system of De Vos and coworkers, a wider search for effective additives both to suppress the catalase type activity of the Mn-tmtacn complexes and to promote ds-dihydroxylation was initiated. An early success was the strongly enhanced ds-dihydroxylation activity observed using [Mn203(tmtacn)2] (Pp6)2 (6) (Figure 11.2) in the combination with aldehydes such as glyoxylic add methylester methyl hemiacetal (gmha (33), Scheme 11.13) [94k]. 

More recently, the use of glyoxylic acid methyl ester hemiacetal as a cocatalyst was shown to afford an even more effective epoxidation catalyst, enabling high conversions with only a 30% excess of hydrogen peroxide. Interestingly, the corresponding cfs-diols were observed as by-products in many cases and a concerted mechanism via a manganese(III)-cfs-diol complex was proposed to explain their formation. 

Another mechanistic interpretation of the Mukaiyama aldol invokes an ene reaction pathway accounting for bond formation. Following complexation, the ene reaction occurs via the organized chair-like transition state 16, providing the syn-stereochemistry observed in the adduct 17. Steric interactions between the methyl group and the glyoxylate ester result in the... 

Condensation of glyoxylate with acetyl-CoA, similar to the formation of citrate (which means addition of the methyl group of acetate to the carbonyl group), resulting directly in the formation of malate. 

---