Carbalkoxy group

Potassium and sodium borohydride show greater selectivity in action than lithium aluminium hydride thus ketones or aldehydes may be reduced to alcohols whilst the cyano, nitro, amido and carbalkoxy groups remain unaffected. Furthermore, the reagent may be used in aqueous or aqueous-alcoholic solution. One simple application of its use will be described, viz., the reduction of m-nitrobenzaldehyde to m-nitrobenzyl alcohol ... 

COCH3 >—CN >—COOR >—Cl >—CH2Y >—OCOCH3 >—OR. The effect of a second 1-substituent is roughly additive. 2-Chlorobutadiene and 2,3-dichlorobutadiene [not included in Table XX] are the most reactive monomers examined. A methyl group usually increases reactivity (methyl methacrylate >methyl acrylate, methacrylonitrile > acrylonitrile, methal-lyl>allyl derivatives) and two chlorine atoms are nearly as effective as a carbalkoxy group. 

Substituting a formyl, carboxy, or carbalkoxy group into a thieno-thiophene or selenophenothiophene molecule has no substantial effect on Ae coupling constants but considerably affects the chemical shifts (see Litvinov and Fraenkel and Michael and Gronowitz ). The chemical shifts of the protons in the selenophene ring are characteristic of different t rpes of condensation of the thiophene and selenophene rings and increase in the order 15 > 14 > 16 irrespective of the solvent used (acetone, CCIJ. A similar sequence is observed in the carbonyl derivatives of the isomeric selenophenothiophenes. 

Cleavage of amino acid esters occurs at both C— C bonds (a, b below) next to the nitrogen atom, loss of the carbalkoxy group being preferred (a). The aliphatic amine fragment decomposes further to give a peak at m/z 30. 

The optical properties of chromophores can be varied by means of substituents. Electron donors (e g., alkyl, alkoxy, or substituted amino groups) and electron acceptors (e g., cyano, alkylsulfonyl, or carbalkoxy groups) can intensify fluorescence depending on their position on the chromophore. 

By using a chiral a-oximino ester, an efficient asymmetric induction at the y-position to the carbalkoxy group was noted with several hypervalent iodine reagents, this substrate gave products with varying degrees of yield and diastereo-isomeric selectivity, as illustrated in the following scheme, where R is (— )-8-phenylmenthyl [17] ... 

The presence of an angular carbalkoxy group (e.g., compound XXIV) (34) leads to the primary formation of the trans product. An attempt has been made to ascertain the reasons for these specific directional effects but it has not been successful (35). 

The classic approach to the formation of a fused pyrimidine ring involves cyclization of adjacent amino and cyano (or carbalkoxy) groups. The formation of pyrrolo[3,2-d] pyrimidines, commencing with a suitably substituted pyrrole, follows this route exclusively. Virtually all of the activity using this approach involves the formation of C-nucleosides. 

Tetrahydropyridazines are formed in the Diels-Alder reaction between a diene and an azo compound (Section III,F) and most of the adducts carry a carbalkoxy group at positions 1 and 2. Partial alkaline hydrolysis with subsequent decarboxylation converts these compounds (142) in the A-monosubstituted derivatives (143), ... 

If a co-carbalkoxy group is present in the starting linear compound instead of the halogen atom, a similar procedure allows synthesis of 2,6-dioxo-l,2-azaphosphina-nes 124 by intramolecular cyclocondensation of amidophosphonic ester 125 [167],... 

Another classic approach to thiophenes is that of Hinsberg, where an alpha-diketone and a sulfide with two methylene groups activated by carbalkoxy groups are reacted in the presence of sodium ethoxide in a double aldol condensation (Scheme 9.12). If the carbalkoxy groups are not desired in the final product, they can be hydrolyzed with NaOH acidification then gives the free di-acid, which can be decarboxylated thermally. 

The nomenclature of this class of compounds is not at all clear. For example, the following names can be found in the literature hydroxamic acid chlorides, hydroxamic chlorides, hydroximic chlorides (Beilstein lists them as Hydroximsaure chloride ), and acyl and aroylchloride oximes. The latter names are used by Chemical Abstracts, Although the name benzoyl chloride oxime for benzhydroxamoyl chloride is formally correct, it does not reflect the close relationship between hydroxamoyl chlorides and hydroxamic acids, their hydrolysis products. In order to be consistent with the nomenclature used in the earlier chapters, I prefer the term hydroxamoyl to hydroxamic chloride. The interrelationship of the halides with the corresponding acids is shown below, and R is representative of the alkyl, aryl, acyl, aroyl, and carbalkoxy group. 

C-De-tert-butylation, preferential 31, 78 Decarbalkoxylation s. a. Replacement of carbalkoxy groups by hydrogen C-Decarbalkoxy ation 29, 499s31 -, ring closure with - 17, 902 Decarbonylation... 

Startg. malonate treated with /-Pr2NLi in THF containing TMEDA at 0° for 3 h, and acidified with 10% HCl - product. Y 75%. F.e. and isolation of P, y -ethylene-P-dicarboxylic acids and esters via 1,2-carbalkoxy group migration, also 2-vinyl-1,4-naphthoquinones, s. C. Mahidol et al., J. Chem. Soc. Chem. Commun. 1988, 1382-3. 

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