Glyoxalic acid, esters

Two strategies have been developed for the preparation of esters of diazoacetic acid. If the alcohol is inexpensive, it is first converted (diketene) into the corresponding acetoacetate (120 equation 49). Diazo transfer with subsequent deacylation then yields the diazoacetate (121). If the alcohol is particularly valuable or sensitive, it may alternatively be esterified with a more direct precursor to diazoacetate. One reagent that has been used for this purpose is glyoxalic acid 2,4,6-triisopropylbenzenesulfonylhydrazone (TIPPS) (123 equation 50). Esterification of the alcohol (122) with (123), using dicyclohexylcarbo-diimide followed by addition of 4-dimethylaminopyridine, gives the diazoacetate (124). ... 

Methyl glyoxylate and ( )-3-hexenol produce the acctoxyalkoxyacetic acid ester 4 in a two-step sequence. Cyclization of the glyoxal derivative 4 in the presence of tin(IV) chloride gave the tetrahydropyranylcarboxylate 5 in 83% yield after 6-endo reaction and chloride ion attack27. Tetrahydropyran 5 shows defined relative stereochemistry at all three asymmetric carbon centers. 

Another method was found by Ok et al. (1988) for diazoacetates involving esters derived from valuable or sensitive alcohols (2-53). The corresponding alcohol (2.115) is esterified with glyoxalic acid 2,4,6-triisopropylbenzenesulfonyl hydrazone (2.116, TIPPS), using dicyclohexylcarbodiimide (DCC) for condensation, followed by the addition of 4-(dimethylamino)pyridine (4-DMAP). 

Acetic acid, oleyl ester. See Oleyl acetate Acetic acid, oxo-. See Glyoxalic acid Acetic acid palladium salt Acetic acid palladium (2+) salt. See Palladium diacetate Acetic acid pentyl ester. See Amyl acetate Acetic acid, phenyl-, butyl ester. See Butyl phenylacetate... 

More than 15 preparations described in patents are variations of the above synthetic schane. hi particular, to obtain optically pure Emtricitabine, lipase-catalyzed enzymatic resolution, as well as chiral stationary phase HPLC was used [143]. However, the most effective procedure included separation of menthyl derivatives. This method evolved significantly since the first publication (which in fact relied on separation of all the 4 possible diastereomers) [144] one of the recent multigram preparations is shown in the Scheme 37 [145]. The first step of the synthesis included formation of methyl ester 159 from glyoxalic acid and L-menthol. Reaction of 159 with 1,4-ditiane 154 gave 1,3-oxathiolane 160 as a mixture of cis diastereomers. 

Polyvinyl alcohols may be applied as such or in crosslinked form [90]. Crosslinkers can be aldehydes (e.g., formaldehyde, acetaldehyde, glyoxal, glutaraldehyde), to form acetals, maleic acid or oxalic acid to form cross-linked ester bridges, or others (e.g., dimethylurea, polyacrolein, diisocyanate, divinyl sulfonate) [89,91]. 

Glyoxal-sodium bisulfite, 30, 86 Glyoxylic acid, w-butyl ester, 35, 18 ethyl ester, diethyl acetal, 35, 59 Grignard reaction, addition to ethyl sec-butylidenecyanoacetate, 35, 7 allylmagnesium bromide with of,(3-di-bromoethyl ethyl ether, 36, 61 allylmagnesium chloride with a,/3-di-bromoethyl ethyl ether, 36, 63 ethylmagnesium bromide with tin tetrachloride, 36, 86... 

Hinsburg first reported that various a-dicarbonyl compounds (256) condensed with thiodiglycolic esters in the presence of alcoholic sodium ethoxide to give various substituted thiophene-2,5-dicarboxylic esters (257). R1 and R2 in (256) could be H, OH, alkyl, OR, aryl or carboxyl groups o-quinones will also condense. If the condensation is carried out in aqueous alcohol, as is the case when glyoxal (256 R1 = R2 = H) is used, the thiophene-2,5-dicarboxylic acid is isolated directly. Pyruvic acid gives the half-ester of (257 R1 = Me, R2 = OH). The earlier work has been reviewed (52HC(3)l). 

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