Michael, Michael-aldol and Michael-Michael reactions of enolate equivalents of butane-2,3-diacetal protected glycolic acid derivatives

Consecutive coupling reactions of butane-2,3-diacetal protected glycolic acid derivatives with Michael acceptors and aldehydes are reported. An enantiopure sample of this building block was used to kinetically resolve a chiral Michael acceptor present as a racemic mixture of enantiomers.     

Anti-selective aldol reactions with titanium enolates of N-glycolyloxazolidinethiones

[reaction: see text] A highly diastereoselective anti aldol addition utilizing a variety of N-glycolyloxazolidinethiones has been developed. Enolization of an N-glycolyloxazolidinethione with titanium (IV) chloride and (-)-sparteine followed by addition of an aldehyde activated with additional TiCl(4) resulted in highly anti-selective aldol additions, typically with no observable syn isomers. Allyl-protected glycolates demonstrated the highest levels of selection and yields, although O-benzyl and O-methyl glycolyloxazolidinethiones also performed well.     

The regioselectivity in the reactions of N-aryl-C-ethoxycarbonylnitrilimines with acrylic acid derivatives

The cycloaddition of a series of C-ethoxycarbonyl-N-arylnitrilimines 5a-f to acrylic acid derivatives namely acrylamide, acrylonitrile and ethyl acrylate has been studied. Under thermal conditions 1,3-dipolar cycloadditions proceed with complete regioselectivity to give 5-R substituted 2-pyrazolines 8–10 in high yield. The structures of the cycloadducts 8–10 were confirmed by ¹³C nmr, ¹H nmr and ir spectra. The regioselectivity is interpreted in terms of HOMO(nitrilimine)-LUMO(dipolarophile) interaction.     

Michael addition-elimination reactions of chiral enolates with ethyl 3-halopropenoates

Key dienoic or dienal substructures of cytotoxic macrolides amphidinolide E and dictyostatin have been prepared via a Michael addition (followed by elimination of X-) of chiral enolates on beta-halo derivatives of ethyl acrylate, with full retention of the initial E or Z configuration. Evans oxazolidin-2-ones and our related thiazolidin-2-ones, as well as a fine-tuning of the reaction conditions, have been essential. Many chiral building blocks are accessible from these adducts.     

Reactions of Weinreb amides: formation of aldehydes by Wittig reactions

Aldehydes are prepared in excellent yield by Wittig reactions of phosphoranes on the Weinreb amide of formic acid followed by in situ hydrolysis.     

苯并单氮杂15-冠-5-与α, β-不饱和羰基化合物的 Michael加成

本文报道借Michael加成使苯并单氮杂15-冠-5与α,β-不饱和羰基化合物反应,合成了氮支套索冠醚(1,2)和酯型双冠醚(3,4)。并提供了合成酯型双冠醚的一种方法,该法条件温和,操作简便,收率高。产物均经IR,^1HNMR和MS鉴定。     

Copolymerization of acrylic acid amides with alkenyl halides

The binary radical copolymerization of acrylic acid amides (acrylamide and N-cyclohexen-1-ylacrylamide) with alkenyl halides (vinyl chloride, vinyl bromide, and allyl chloride) has been studied. The constants of relative activity of the monomers used are calculated. For the systems under investigation, the occurrence of dehydrochlorination of a polymer chain and protonation of a carbonyl group occur is confirmed. Allyl chloride shows the most pronounced tendency toward dehydrochlorination, while in the case of vinyl chloride, this tendency is the least distinct. The polymer-analogous transformations result in copolymers containing polyene fragments and units of ammonium or oxonium amide salts.     

Intramolecular Michael reactions of aliphatic aldehyde enolates generated by imidazolium carbenes

Due to the high reactivity of the formyl group under either basic or acidic reaction conditions required for the direct generation of aldehyde enolates, intramolecular Michael additions of aldehyde enolates to α,β-unsaturated carbonyl compounds have been underexplored for the stereoselective synthesis of carbocyclic compounds. The intramolecular Michael reaction of aldehyde enolates generated by imidazolium carbenes was explored for the synthesis of cyclopentane aldehydes. The imidazolium carbenes were used as Brønsted bases to directly generate the aldehydes enolates.     

Enantioselective organocatalytic Michael additions to acrylic acid derivatives: generation of all-carbon quaternary stereocentres

Acrylic esters, thioesters and N-acryloyl pyrrole have been identified as effective electrophiles in the enantioselective Michael addition reaction with beta-keto ester pro-nucleophiles catalysed by a cinchona alkaloid derived bifunctional organocatalyst; enantiomeric excesses of up to 98% and yields of up to 96% can be obtained for a range of Michael acceptors and pro-nucleophiles.     

Enantioselective solution- and solid-phase synthesis of glutamic acid derivatives via Michael addition reactions

The enantioselective conjugate addition of Schiff base ester derivatives to Michael acceptors either in solution (56–89% e.e.) or on solid-phase (34–82% e.e.) gave optically active unnatural α-amino acid derivatives. The reaction was conducted in the presence of chiral, non-racemic quaternary salts derived from the cinchona alkaloids using neutral, non-ionic phosphazene bases.     

Tetramic acid and imidazolidinone syntheses via unexpected base induced cyclisations of alanine derived Weinreb amides

Reactions of N-protected derivatives of Weinreb amides of alanine with strong base unexpectedly gave tetramic acid derivatives or an imidazolidinone. The tetramic acid derivatives were obtained by unusual cyclisation of N-acyl N-methoxy derivatives of alanine Weinreb amide upon treatment with potassium hexamethyldisilazide and benzyl bromide. In contrast, treatment of a bromobenzylidine alanine Weinreb amide with potassium hexamethyldisilazide gave rise to cyclisation to form an imidazolidinone.     

Highly stereoselective aldol reactions of titanium enolates from lactate-derived chiral ketones

[reaction: see text] Highly stereoselective titanium-mediated aldol reactions based on lactate-derived ketones are reported. The stereochemical outcome of the process depends on the protecting group (PMB or Bn) and the Lewis acid (i-PrOTiCl(3) or TiCl(4)) used in the enolization step, the corresponding anti-syn or syn-syn aldols being prepared in high yields and with diastereomeric ratios up to 99:1.     

Acetals of lactams and acid amides. 46. Unusual reactions of α-cyano-β-dimethylaminocrotonamide with anthranilic acid derivatives

It has been shown that the reaction of the enaminoamide -cyano--dimethylaminocrotonamide with anthranilic acid and its ethyl ester unexpectedly gives quinazoline-2,4-dione and 2-methyl-3-cyano-4-quinolone, respectively. The structures of the products were confirmed by their spectra and by direct synthesis.For communication 45, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 84–87, January, 1986.     

Formation of quaternary stereocenters by copper-catalyzed Michael reactions with L-valine amides as auxiliaries

Extensive investigations of chiral auxiliaries and active metals for Michael addition of 1,3-dicarbonyl compounds with vinyl ketones are summarized. Our efforts result in a widely applicable auxiliary-mediated, copper(II) acetate-catalyzed procedure. For these purposes, L-valine diethylamide is an optimal chiral auxiliary giving quaternary stereocenters with up to 99 % ee at ambient temperature. No inert or anhydrous conditions are required, the solvent is simply acetone, and the auxiliary can be recovered almost quantitatively after workup.     

Asymmetric synthesis of beta-amino carbonyl compounds with N-sulfinyl beta-amino Weinreb amides

[reaction: see text] Diverse organometallic reagents readily add to enantiopure N-sulfinyl beta-amino Weinreb amides providing the corresponding, stable, N-sulfinyl beta-amino carbonyl compounds in good to excellent yields. This new methodology represents a general solution to the problem of beta-amino carbonyl syntheses, which are important chiral building blocks and constituents of natural products. N-Sulfinyl beta-amino Weinreb amides are prepared by reaction of the potassium enolate of N-methoxy N-methylacetamide with sulfinimines (N-sulfinyl imines) or lithium N,O-dimethylhydroxylamine with N-sulfinyl beta-amino esters.