Glyoxylates menthyl

Zamojski and coworkers have explored the use of the furan-carbonyl photocycloaddition in asymmetric synthesis, with somewhat limited success88. Irradiation of chiral glyoxylate derivative 196 [R = (R)(—)-menthyl and (R)(—)-8-phenylmenthyl] afforded... 

Condensation of the mixture of dienes 661 and 662 with 2(R)-menthyl glyoxylate (until only the trams,trams diene had entered into reaction) gave1153 a mixture of three products (667-669) in 63% overall yield. This mixture was separated into its components. Reduction of R1 to a hydroxymethyl group in 667 and 668, and m-hydroxylation of the double bond, gave disaccharides 670 and 671, in which the newly created sugar units were identified as D- and L-gulose, respectively. 

The procedure has been employed for the synthesis of the determinant trisaccharide unit of the human blood group A using 2-28 and the (-)-menthyl glyoxylate 2-27 as a matched pair to give the desired disaccharide 2-30 after isomerisation of the primarily obtained mixture of 2-29 and 2-30. 

An asymmetric synthesis of alanine itself is provided by the Grignard reaction of the benzylamine Schiff base, 57, of ( —)-menthyl glyoxylate, 56. The (S)-alanine, 58, was obtained with a 53% optical yield [71]. This yield could be influenced by another... 

Related Reagents. 8-Phenylmenthyl Crotonate 8-Phenyl-menthyl Glyoxylate 8-Phenylmenthyl Pyruvate. 

Double asymmetric reduction of (-)menthyl pyruvate and (-)menthyl phenyl-glyoxylate uses rhodium(I) complexes with (-I-)DIOP or ( —)DIOP as cataJysP . Although only a slight effect of (— )menthyl group on the asymmetric induction is observed in the case of (— )menthyl pyruvate, i.e., (+ )DIOP, 85.6% d.e., S (— )DIOP, 82.8%... 

Two groups have investigated N-sulfonyl imines of glyoxylate esters, derived from scalemic alcohols, in Diels-Alder reactions [67b, 73]. Prato and coworkers reported that glyoxylate N-sulfonyl imines bearing (-)-menthyl, (-)-bornyl and (-)-8-phenylmethyl auxiliaries reacted with cydopentadiene either thermally or using Lewis acids to give only very modest diastereomeric product ratios (56 44, 53 47,60 40, respectively) [67b]. 

Achmatowicz examined asymmetric induction in the ene reactions of (-)-menthyl glyoxylate with 1-pentene and found modest asymmetric induction of 5-30%. The configuration of the new center in the adducts was (S) with SnCU, BF3 and TiCU and (/ ) with AICI3. In mariced contrast to these results. 

TiCU-mediated addition of silyl enol ether (95) to chiral a-amino aldehyde (94) was reported to proceed with good chelation control, albeit in poor yield (equation 28). Effective chelation control was also reported in the TiCU-mediated reactions of chiral a-alkoxy and p-alkoxy acyl cyanides (96) and (97) with silyl enol ether (95 equations 29 and SO). Reaction of acyl cyanide (97) with the ( )-silyl enol ether (93) gave a single stereoisomer as a result of complete chelation control and syn simple stereoselection (equation 31). Additions of silyl enol ethers and silyl ketene acetals to (-)-menthyl phenyl-glyoxylate and pyruvate were reported to proceed with moderate facial selectivity the best result (84 16) is shown in equation (32). ... 

Addition of (/ )-menthyl glyoxylate (la) to 1-trimethylsilyloxy-l,3-butadiene (2e) proceeds with a selectivity comparable to that of 1-alkoxybutadicnes. Even (f )-8-phenylmenthyl glyoxylate (1 b), bearing a very efficient chiral auxiliary, adds to 1-trimethylsilyloxy-l,3-butadiene (2e) with low diastereoselectivity17. 

High pressure cycloaddition of (f )-menthyl glyoxylate (la) and symmetric 1,3-dienes 2,3-dimethyl-1,3-butadiene (7) and 1.3-cyclohexadiene (10) has been studied1S. Diastereoselectivi-ties higher than those for 1-methoxy-1,3-butadiene (2a) are obtained, but are still below a d.r. of 62.5 37.5. Obviously, the [4 + 2] cycloaddition of glyoxylates requires a very efficient chiral auxiliary (see Section 1.6.1.1.3.2.2.). 

A high-pressure apparatus is filled with a mixture of 1.6 g (5 mmol) of (7 )-menthyl glyoxylate (1 a). 0.82 g (10 mmol) of 2,3-dimethyl-l, 3-butadiene (7) and 10 mg of hydroquinone in 10 mL of CH2C1, and the pressure is slowly elevated to 6.2 x 106 Torr at 20 CC. After stabilization of pressure, the reaction mixture is kept under these conditions for 20 h. After decompression, the solvent is evaporated, the residue is dissolved in 50 mL of hexane, and the solution is filtered to remove small amounts of polymers. The filtrate is concentrated under reduced pressure and the residue is chromatographed (silica gel. ligroin Et20 9 1) to give adducts 8 and 9 yield 680 mg (46%). 

Introduction of the additional chiral auxiliary into the dtenophile molecule by choosing L-menthyl glyoxylate (2b) neither improves the endojexo selectivity (albeit for the inositol derived diene lb where a predominance of c.vo-adducts has been found) nor the selectivity at C-525 2S. 

Menthyl glyoxylate has been used in an attempt to induce asymmetry during a Diels-Alder reaction between the aldehyde group of the glyoxylate and a... 

Reduction of the a-keto ester of an optically active alcohol, followed by hydrolysis of the a-hydroxy ester which results, yields an optically active a-hydroxy acid. Sixty years ago, for example, McKenzie (1904) reduced optically active (—)-menthyl phenyl-glyoxylate with aluminum amalgam in moist ether and obtained unequal amounts of diastereomeric (—)-menthyl mandelates. Saponification, however, gave racemic mandelic acid. Later work (McKenzie and Humphries, 1909) showed that racemization could be avoided by acetylation of the intermediate mandelate before saponification, and that reduction of (—)-menthyl phenylgly-oxylate produced mandelic acid having an excess of the R- —) enantiomer [Eq. (5)]. 

David s group have applied their diene approach to disaccharides to the synthesis of kasuganobiosamine (30). Cycloaddition of the dienyl ether (31) with menthyl glyoxylate gave a glycal which was converted to the glyceno-sidulose (32) which, in turn, led to (30) by sequential hydrazoic acid addition, oximation, reduction, and deblocking. ... 

Pyrans.— High-pressure [4 + 2] cycloaddition of i -(-)-menthyl glyoxylate and 2,3-dimethylbuta-l,3-diene has been studied, and although it was found that optical yields varied with pressure, the adduct had the (2f )-configuration regardless of pressure (Scheme 36). The [4 + 2] cycloaddition of unsaturated carbonyl compounds to vinyl ethers gives substituted dihydropyrans, a reaction also favoured by increased pressure (Scheme 37). ... 

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