Iodomethaneboronic esters and aminomethaneboronic esters

An efficient preparation of pinacol iodomethaneboronate and dibutyl iodomethaneboronate from the respective (phenylthio)methaneboronic esters has been devised, using the reaction with methyl iodide. Pinacol iodomethaneboronate reacts efficiently wit tertiary amines to form the crystalline quaternary ammonium salts. Dibutyl iodomethaneboronate reacts with excess piperidine or morpholine in ether to precipitate piperidine or morpholine hydriodide and yield the distillable piperidino- or morpholinomethaneboronic ester. Benzylamine failed to yield a stable product.     

Diastereoselective synthesis of aziridine esters via amino selanyl esters

A synthesis of aziridine esters based on the cyclisation of amino selanyl esters induced by the selanyl group activation was developed with either the Meerwein salt or NBS. Two asymmetric approaches are proposed: the diastereoselective reductions of α-selanyl β-iminoesters derived from α-oxoesters, which lead to cis chiral aziridine esters 6 and 6′; and the diastereoselective conjugate additions of a chiral amide to α,β-unsaturated esters providing trans chiral aziridine esters 6 and 6″.     

Deconjugative conversion of alpha-alkynyl esters to alpha,alpha-disubstituted beta-alkynyl esters

We report the development of a method for the conversion of a variety of conjugated alpha-alkynyl esters to alpha,alpha-disubstituted beta-alkynylesters through the use of strong amide bases. Studies indicate that the second equivalent of base leads to the dianion intermediate. Optimal conditions included the use of 2 equiv of lithium diisopropylamide in THF with HMPA as the cosolvent followed by trapping with a variety of carbon electrophiles. Trapping with bis-electrophiles leads to spiro cycloalkane products.     

Copper-catalyzed enantioselective Henry reactions of alpha-keto esters: an easy entry to optically active beta-nitro-alpha-hydroxy esters and beta-amino-alpha-hydroxy esters

The catalytic enantioselective Henry reaction of alpha-keto esters with nitromethane has been developed. The reaction conditions have been optimized by the screening of different chiral Lewis acids, solvents, and bases, and it was found that the copper(II)-tert-butyl bisoxazoline complex in combination with triethylamine catalyzed a highly enantioselective reaction giving optically active beta-nitro-alpha-hydroxy esters in high yields and with excellent enantiomeric excesses. The scope of the reaction is demonstrated by the reaction of a variety of different alpha-keto esters. The catalytic enantioselective Henry reaction of beta,gamma-unsaturated-alpha-keto esters proceeds as a 1,2-addition reaction exclusively, in contrast to the uncatalyzed reaction where both the 1,2- and 1,4-addition products are formed. It is demonstrated that the beta-nitro-alpha-hydroxy esters can be converted into, e.g., Boc-protected beta-amino-alpha-hydroxy esters in high yields and without loss of optical purity. The mechanism for the reaction is discussed, and it is postulated that both the alpha-keto ester and nitromethane/nitronate is coordinated to the metal center during the reaction course.     

Palladium-catalyzed preparation of α-allyl esters and α,β-unsaturated esters from saturated esters via their silyl acetals

Reaction of ketene silyl acetals with allylic carbonates in the presence of palladium-phosphine catalyst in dioxane gives α-allyl esters in high yields. When the reaction is carried out with phosphine-free palladium catalyst in nitriles, α,β-unsaturated esters are obtained in good yields.     

Palladium-catalysed arylation of acetoacetate esters to yield 2-arylacetic acid esters

The coupling reaction between ethyl acetoacetate and a number of aryl halides in the presence of palladium acetate, a bulky and electron rich phosphine and K₃PO₄ is described. The arylated acetoacetate ester is de-acylated under the reaction conditions resulting in the generation of 2-arylacetic acid esters, constituting a mild alternative to direct arylation of carboxylate esters.     

Stereoselective synthesis of functionalized gamma-amino esters: azetidinium salts and epoxy esters

Addition of several lithium ester enolates to chiral 1-aminoalkyl chloromethyl ketones 1 affords enantiomerically pure 3-hydroxyazetidinium salts 3 or 3-(1'-aminoalkyl)-3,4-epoxy esters 4, depending on the reaction conditions. [reaction: see text]     

脂肪酶催化合成L-抗坏血酸脂肪酸酯和D-异抗坏血酸脂肪酸酯

用固定化脂肪酶Lipozyme 435作催化剂,分别用直接酯化法和酯交换法合成L-抗坏血酸脂肪酸酯和D-异抗坏血酸脂肪酸酯.产物结构经IR、1HNMR、13CNMR和MS表征.结果表明,对于同一目标化合物,相似条件下,直接酯化法的效果优于酯交换法,原料脂肪酸和脂肪酸甲酯均可回收循环使用.     

Synthesis of regioselectively brominated cellulose esters and 6-cyano-6-deoxycellulose esters

The control of regiochemistry in the synthesis of polysaccharide derivatives is one of the most significant scientific challenges in the field. Its importance is only further highlighted by the individual successes in synthesis of regioselectively substituted derivatives, in particular cellulose esters and ethers, over the last 20 years. The availability of these samples and studies of their properties versus randomly substituted analogs has shown clearly that properties like solubility, aggregation phenomena, and optical properties depend heavily on the regiochemistry of substitution. We report here on the one-pot synthesis of novel 6-bromo-6-deoxy-2,3-O-acylcellulose derivatives, which as more organic soluble derivatives of 6-bromo-6-deoxycellulose should allow broader exploitation of the highly regioselective cellulose 6-bromination chemistry. We illustrate the potential of these new derivatives by conversion to 6-cyano-6-deoxycellulose esters.     

Transesteeification of malonic esters

Conclusions Hither esters of malonic acid have been prepared in good yield by transesterification of lower esters with appropriate primary or secondary alcohols in the presence of alkaline or acid catalysts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 892–895 (1968).     

Transacylation of alpha-aryl-beta-keto esters

The acyl group of an alpha-aryl-beta-keto ester was readily transferred to N-, O-, and S-nucleophiles. The transacylation from arylated diethyl 3-oxoglutarate to amines led to unsymmetrical malonic acid amide esters in high yields. The present reaction proceeded under mild conditions without formation of detectable byproducts. Only simple experimental manipulations were required. This reaction was also found to be sensitive to steric factors, which enabled the chemoselective monoacylation of diamines and amino alcohols without any modifications such as protection.     

Preparation of lupinine esters

Conclusions A number of lupinine esters and their methiodides were synthesized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 728–730, March, 1972.