Ester glyoxylate

Similar transformations have been performed with Danishefsky s diene and glyoxylate esters [85] catalyzed by bis (oxazoHne)-metal complexes to afford the hetero Diels-Alder product in 70% isolated yield and up to 72% ee. Jorgensen [86,87] reported a highly enantioselective, catalytic hetero Diels-Alder reaction of ketones and similar chiral copper(II) complexes leading to enantiomeric excesses up to 99% (Scheme 31, reaction 2). They also described [88] a highly diastereo- and enantioselective catalytic hetero Diels-Alder reaction of /I, y-imsaturated a-ketoesters with electron-rich alkenes... 

Coumestrol has been prepared via a photocyclization of the glyoxylate ester shown below through consecutive 5-hydrogen abstraction and cyclization processes, and is followed by... 

Ghosh et al. (228) investigated the cycloaddition of Danishefsky s diene (1-methoxy-3-trimethylsiloxybutadiene, 334) and glyoxylate esters. The reaction provides a mixture of the Mukaiyama aldol product (336) and dihydropyrone (335). Treatment of the unpurified reaction mixture with trifluoroacetic acid induced the cyclocondensation to provide dihydropyrone (335) in 70% combined yield and 72% ee, Eq. 188. 

The considerable Lewis acidity of bis(oxazoline)-copper(II) complexes held promise for catalyzing the ene reaction, a process that usually requires strong Lewis acids. Indeed, these catalysts effect a highly selective ene reaction between a variety of alkene partners and glyoxylate esters to produce a-hydroxy esters in good yield, Eq. 210 (245). The ene reaction between cyclohexene and ethyl glyoxylate proceeds in excellent diastereoselectivity and enantioselectivity, Eq. 211. As a testament to the Lewis acidity of these complexes, it is noteworthy that... 

Other examples of efficient enzymatic resolutions by reaction at a remote position from stereocentres have been reported, such as the lipase-catalysed resolution of a synthetic intermediate of escitalopram." This property of enzymes has also been effectively used to resolve sterically hindered compounds by the introduction of a tether so that the enzyme-catalysed reaction can be performed at an artificially created, but less hindered, remote location. An example is the resolution of tertiary alcohols by the introduction of a glyoxylate ester. 

Or, alternatively (see Scheme 3.3), the immediate precursor of patulin could be iO, arriving through this new route to tetrahydro-y-pyrone 12, as the starting material, together with the synthon =CH-COOR, which conveniently elaborated gives either a glyoxylic ester, OCH-COOR, or an oxomalonic diester. 

Reduction of nitro glyoxylic ester 334 with iron powder in acetic acid into pyrrolo-benzothiadiazepine 335 represents a type (i) intramolecular cyclization (Equation (39) (1996JHC2019)). 

The nitriles can also be employed as intermediates in the condensation of ethyl glyoxylate with aJdehydo sugars under the influence of sodium methoxide, leading to the preparation of L-ascorbic acid and similar compounds. Helferich and Peters described the synthesis of D-ascorbic acid (XXVIII) from tetraacetyl-n-xylononitrile (XXVI) presumably the nitrile underwent a type of ZempMn degradation and the n-threose (XXVII) thus formed condensed with the glyoxylic ester. The method... 

Using a diene, the reaction can proceed through the ene pathway as above, or through the hetero-Diels-Alder pathway. For example, the condensation of 2,3-dimethyl-1,3-butadiene 103 with glyoxylate esters 99, 104, and 105 can proceed to form either a hetero Diels-Alder cycloadduct 106 or an ene product 107 (Fig. 9.35). 

TABLE 9.18. HETERO-DIELS-ALDER REACTION OE DANISHEFSKY S DIENE WITH GLYOXYLATE ESTERS"... 

TABLE 9.18 HETERO DIELS-ALDER REACTION OF DANISHEFSKY S DIENE WITH GLYOXYLATE ESTERS, 558... 

Water-soluble biodegradable polycarboxylates with an acetal or ketal weak link were inventions of Monsanto scientists in the course of their search for biodegradable deteigent polymers. However, the polymers were prevented by economics from reaching commercial status. The polymers are based on the anionic or cationic polymerization of glyoxylic esters at low temperature (molecular weight is inversely proportional to the polymerization temperature) and subsequent hydrolysis to the salt form of the polyacid, which is a hemiacetal (R = H) or ketal (R = CH3) if methylglyoxylic acid is used, and stable under basic conditions. 

Because of the lack of ready access to 2, Whitesell et al.2 recommend trans-2-phenylcyclohexanol (3) as an auxiliary. Hydrolysis of the acetate of ( + )-3 with hog liver esterase provides optically pure (- )-3,aD - 56° and (+ )-3,aD + 54°. The glyoxylate ester of 3 undergoes ene reactions with high diastereoselectivity. 

A full account5 describes the enantioselective carbonyl-ene reaction of glyoxylate esters catalyzed by a binaphthol-derived chiral titanium complex that is potentially useful for the asymmetric synthesis of a-hydroxy esters of biological and synthetic importance.6 The present procedure is applicable to a variety of 1,1-disubstituted olefins to provide ene products in extremely high enantiomeric purity by the judicious choice of the dichloro or dibromo chiral catalyst (see Table). In certain glyoxylate-ene reactions involving removal of a methyl hydrogen, the dichloro catalyst... 

Except for the well-documented conjugate additions of diethylaluminum cyanide,92 triethylaluminum-hydrogen cyanide and Lewis acid-tertiary alkyl isonitriles,93 examples of Lewis acid catalyzed conjugate additions of acyl anion equivalents are scant Notable examples are additions of copper aldimines (233),94, 94b prepared from (232), and silyl ketene acetals (234)940 to a,(3-enones which afford 1,4-ketoal-dehydes (235) and 2,5-diketo esters (236), respectively (Scheme 37). The acetal (234) is considered a glyoxylate ester anion equivalent. 

Asymmetric reactions of a chiral glyoxylate ester. Grignard reagents add to the glyoxylate ester (2) of ( — )-l with unusually high asymmetric induction. The chirality... 

An hDA reaction between Danishefsky s diene and glyoxylate esters proceeds in the presence of bisoxazoline-lanthanide complexes with moderate levels of enantioselectivity <2000TL2203>. A similar reaction between Danishefsky s diene and a-keto esters proceeds with excellent enantioselectivity in the presence of bisoxazoline-copper <2001TL6231, 2003EJ0317, 2004TA1987> or Cr(m), Co(n and m)-salen complexes <2004TA3189>. 

The choice of solvent has had little, if any, influence on the majority of Diels-Alder reactions.210,211 Although the addition of a Lewis acid might be expected to show more solvent dependence, generally there appears to be little effect on asymmetric induction.118129 However, a dramatic effect of solvent polarity has been observed for chiral metallocene triflate complexes.212 The use of polar solvents, such as nitromethane and nitropropane, leads to a significant improvement in the catalytic properties of a copper Lewis acid complex in the hetero Diels-Alder reaction of glyoxylate esters with dienes.213... 

In the reaction of the first glyoxylate ester with furan, we could obtain the observed diastereoisomer (1 R,1R,5S,6S) (Fig. 3.184) and the other one (I RJS,-5R,6R). These two stereoisomers showed a different energy for 0.07 kcal mol-1, with the most stable one being the (1 R,1R,5S,6S) isomer. In the reaction of the... 

The aldehyde products formed from glyoxylate esters not only absorb light but are highly reactive substrates for attack by excited ketones and can be depleted by over-irradiation. 

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