A-Alkoxycarboxylic acids

Combination of the coordinating ability of metal ions for hydroxy group containing compounds with the before mentioned exceptional behaviours of DBTA in chiral recognation processes gave us a new possibility for direct resolution of a-alkoxycarboxylic acids, a-hydroxycarboxylic acid esters and series of racemic alcohols... 

Optical resolutions of two a-alkoxycarboxylic acids (3a and 3b, Scheme 3) were accomplished with the neutral calcium salt of DBTA (DBTACa) in aqueous ethanol solution. [24] Preparation of the diastereoisomers is quite simple a stoichiometric mixture of DBTA monohydrate and calcium oxide had to solve in hot aqueous ethanol to form DBTACa salt and then racemic acid (3a or 3b) had to add into it. On cooling [Ca(H20)(f -3a)]DBTA.H20 or [Ca(H20)(S-3b)]DBTA.H20 cystallised. Free (S)-3a or (R)-3b was obtained from the corresponding filtrate. In the schemes and the formulas (6) or (R) stands for showing the configuration of the of the major enantiomer in the product. For example, (.S )-3a means that the isolated material contained the 6-isomer in excess, ee values are given in the Tables. 

Crowded structure of these diastereoisomers limitate the scope of this resolution method to relatively small racemic a-alkoxycarboxylic acids. Furthermore, the presence of an alkoxy group in the racemate seems to be essential because its oxygen atom also coordinates to the calcium ion. Luck of such coordination hindered formation of crystalline complex when a-chlorocarboxylic acids were tested. On the other hand, a-hydroxycarboxylic acids precipitated from the reaction mixture as simple calcium salts because of their lowest solubility among the possible combinations of the components of the reaction mixtures. 

A unique alkoxymethylation reaction can be acconplished by treatment of a-alkoxycarboxylic acid chlorides with ketones in the presence of Sml2 (equation 28). llie reaction is postulated to proceed by a reductive decarbonylation process, leading to a relatively stable a-alkoxy radical. Addition ctf this radical to the Sm -activated carbonyl and further reduction and hydrolysis provides the observed product. An... 

Dialkylborinyl triflateslethyldiisopropylamine Stereospecific aldol-type condensation with a-alkoxycarboxylic acid esters under mild conditions 5> /f-a-Alkoxy-p-hydroxycarboxylic acid esters... 

A2-l,2,3-triazol-5-ones 43, 161 a-Alkoxycarboxylic acid esters 43, 158 -, aldol-type condensation, stereospecific with - 44, 569... 

Acylamino-1 -thioethers N-Acylcarboxylic acid thioamides Acylisothiocyanates Acylthiocyanates N-Acylthioiminoesters N-a-Alkoxycarboxylic acid thioamides... 

Mixed acetals from a-alkoxycarboxylic acids s. 17, 292 also acetals from ethers by anodic oxidation s. Ghem. Ind. 1965, 39... 

Replacement of carboxyl by alkoxy groups Mixed acetals from a-alkoxycarboxylic acids... 

A -oxazolines 28, 85 a-Acylaminoaldehydes 28, 66 a AcyIamino-a-alkoxycarboxylic acid esters 24, 145 suppl. 28 C-a-Acylaminoalkylation, review 16, 843 suppl, 26 a-Acylaminocarboxylic acid amides... 

Replacement of alkylthio by alkoxy groups a-Alkoxycarboxylic acid esters... 

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