Domino condensation/aza-Michael/O→N acyl migration of carbodiimides with activated α,β-unsaturated carboxylic acids to form hydantoins

Activated α,β-unsaturated carboxylic acids undergo an unexpected domino condensation/aza-Michael/O→N acyl migration with carbodiimides, producing N,N-disubstituted hydantoins in good yields. An array of structurally varied aspartic acid-derived hydantoins, including some fluorinated derivatives, have been synthesized by this method, whose scope and limits are discussed.     

Synthesis of lactams by radical substitution reaction of alpha,beta-unsaturated acyl radicals at amine nitrogen

[reaction: see text] Substitution at nitrogen by alpha,beta-unsaturated acyl radicals took place accompanied by elimination of an alpha-phenethyl radical. This reaction led to the development of a new carbonylative annulation method for five- to seven-membered ring lactams.     

The first cyclopropanation reaction of unmasked alpha,beta-unsaturated carboxylic acids: direct and complete stereospecific synthesis of cyclopropanecarboxylic acids promoted by Sm/CHI3

A samarium-promoted cyclopropanation of unmasked alpha,beta-unsaturated acids is described. This reaction can be carried out on (E)- or (Z)-alpha,beta-unsaturated carboxylic acids. In all cases the process is completely stereospecific and stereoselective. A mechanism has been proposed to explain the cyclopropanation reaction.     

Selective synthesis of alpha,beta-unsaturated ketones by dibutyltin dimethoxide-catalyzed condensation of aldehydes with alkenyl trichloroacetates

Various alpha,beta-unsaturated ketones were stereoselectively synthesized in high yields up to 94% by a condensation reaction between alkenyl trichloroacetates and aldehydes using dibutyltin dimethoxide as a catalyst in the presence of methanol. This process is superior to the classical Claisen-Schmidt condensation with respect to mildness of the base catalyst and product selectivity.     

A convenient synthesis of 2-acyl benzothiazoles/thiazoles from benzothiazole/thiazole and N,N'-carbonyldiimidazole activated carboxylic acids

A convenient and efficient strategy for the synthesis of 2-acyl benzothiazoles/thiazoles has been developed. The treatment of benzothiazole/thiazole with allylic Grignard reagents readily generates the corresponding 2-Grignard reagents, which is followed by a reaction with N,N'-carbonyldiimidazole activated carboxylic acids to afford various 2-acyl benzothiazoles/thiazoles products. The synthetic method is applicable to a wide array of carboxylic acids and allows easy access to 2-acyl benzothiazoles/thiazoles with considerable yields under mild reaction conditions.     

Synthesis of 2-alkylidenetetrahydrofurans by Ru-catalyzed regio- and stereoselective codimerization of dihydrofurans with alpha,beta-unsaturated esters

2-(1-Alkoxycarbonyl)alkylidenetetrahydrofurans were readily synthesized by the codimerization of 2,3- or 2,5-dihydrofurans with alpha,beta-unsaturated esters using a zerovalent Ru catalyst, Ru(cod)(cot), with high regio- and stereoselectivity.     

Synthesis of 3,4-dihydro-2H-pyrans by hetero-Diels-Alder reactions of functionalized alpha,beta-unsaturated carbonyl compounds with N-vinyl-2-oxazolidinone

Cycloadditions of 3-aryl-2-benzoyl-2-propenenitriles and 3-phenylsulfonyl-3-buten-2-one to N-vinyl-2-oxazolidinone proceed regio- and diastereoselectively yielding cis and trans diastereoisomers of 4-aryl-3,4-dihydro-2-(2-oxo-3-oxazolidinyl)-2H-pyrans in 37-65% yield. Cycloadducts cis- were the major products. Reaction of 5-arylidene-1,3-dimethylbarbituric acids with dienophile afforded mixtures of 2H-pyrano[2,3-d]pyrimidine-2,4(3H)-diones trans and products resulted from an elimination of 2-oxazolidinone, in 50-52% yield. To confirm the experimental results, semiempirical AM1 and PM3 calculations of frontier orbital energies have been performed.     

An efficient highly regioselective synthesis of 2,3,4-trisubstituted pyrroles by cycloaddition of polarized ketene S,S- and N,S-acetals with activated methylene isocyanides

An efficient route for regioselective synthesis of 2,3,4- substituted pyrroles allowing precise control over the introduction of a number of substituents and functionalities (tosyl, carbalkoxy, aryl, cyano, nitro, acetyl, benzoyl, cyclic amines, etc.) at the three positions of the pyrrole ring has been developed via 1,3-dipolar cycloaddition of readily accessible polarized ketene S,S- and N,S-acetals with carbanions derived from activated methylene isocyanides.     

Direct reaction of dibromoacetic acid with aldehydes promoted by samarium diiodide: an easy, efficient, and rapid synthesis of (E)-alpha,beta-unsaturated carboxylic acids with total stereoselectivity

A promoted SmI2 direct reaction of dibromoacetic acid with different aldehydes, followed by an elimination reaction also promoted by samarium diiodide, affords (E)-alpha,beta-unsaturated carboxylic acids 2 with total stereoselectivity. A mechanism to explain this transformation is proposed.     

Synthesis of 1-azaxanthones by condensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-(cyano)benzopyrylium triflates and subsequent domino ‘retro-Michael/nitrile-addition/heterocyclization’ reaction

Functionalized 1-azaxanthones (5-oxo-5H-[1]-benzopyrano[2,3-b]pyridines) were prepared by TMSOTf-mediated condensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 3-cyanochromones and subsequent base-mediated domino ‘retro-Michael/nitrile-addition/heterocyclization’ reaction.     

One-pot syntheses of 2,3-dihydrothiopyran-4-one derivatives by Pd/Cu-catalyzed reactions of alpha,beta-unsaturated thioesters with propargyl alcohols

2,3-Dihydrothiopyran-4-one derivatives were readily prepared by Pd/Cu-catalyzed reactions between alpha,beta-unsaturated thioesters and propargyl alcohols in the presence of bases. Of note, both carbon-sulfur bonds were cleaved as a result of the single procedure.     

Oxidative coupling of benzenes with alpha,beta-unsaturated aldehydes by the Pd(OAc)2/molybdovanadophosphoric acid/O2 system

[reaction: see text] The oxidative coupling reaction of benzene with an alpha,beta-unsaturated aldehyde was examined by the combined catalytic system of Pd(OAc)2 with molybdovanadophosphoric acid (HPMoV) under atmospheric dioxygen. Thus, the reaction of benzene with acrolein under dioxygen (1 atm) by the use of catalytic amounts of Pd(OAc)2 and H4PMo11VO40 x 26H2O in the presence of dibenzoylmethane as a ligand in propionic acid at 90 degrees C for 1.5 h afforded cinnamaldehyde in 59% yield and beta-phenylcinnamaldehyde in 5% yield. This catalytic system was extended to the direct oxidative coupling through the C-H bond activation of various arenes with acrolein and methacrolein.     

A green Hunsdiecker reaction: synthesis of beta-bromostyrenes from the reaction of alpha,beta-unsaturated aromatic carboxylic acids with KBr and H2O2 catalysed by Na2MoO4.2H2O in aqueous medium

Reaction of alpha,beta-unsaturated aromatic carboxylic acids with KBr and H2O2 in the presence of Na2MoO4.2H2O in aqueous medium affords beta-bromo alkenes in high yield.     

Synthesis of highly functionalized biaryls by condensation of 2-fluoro-1,3-bis(silyloxy) 1,3-dienes with 3-cyanochromones and subsequent domino "retro-Michael/aldol/fragmentation"

The Me(3)SiOTf-mediated condensation of 1-ethoxy-2-fluoro-1,3-bis(trimethylsilyloxy) 1,3-dienes with 3-cyanochromones afforded 3-cyano-2-(4-ethoxy-3-fluoro-2,4-dioxobutyl)chroman-4-ones. Their reaction with triethylamine afforded fluorinated azaxanthones or biaryls. The product distribution depends on the structure of the diene. The formation of the biaryls can be explained by an unprecedented domino "retro-Michael/aldol/fragmentation" reaction.     

New activation of carboxylic acids by reaction with N,N-bis-(2-oxo-3-oxazolidinyl) phosphorodiamidic chloride (ClsPO)

Pentacoordinated and quinquevalent phosphorus intermediates, have been isolated by reaction between the title reagent and carboxylic acids, prior to conversion into amides.     

Synthesis of 2-trichloromethyloxazolidin-5-ones by reaction of chloral with N,O-trimethylsilyl derivatives of amino acids

The corresponding 2-trichloromethyloxazolidin-5-ones were obtained by reaction of chloral with trimethylsilyl (TMS) derivatives of some amino acids. The corresponding oxazolidin-5-ones could not be obtained by the action of chloral on aspartic and glutamic acids.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1472–1473, November, 1978.     

Synthesis of polyketide-type phenols by domino ‘Michael/retro-Michael/Aldol’ reactions of 3-formylchromones with silyl enol ethers derived from ethyl 3,5-dioxohexanoate

Highly functionalized polyketide-type phenols were prepared by domino ‘Michael/retro-Michael/aldol’ reactions of 3-formylchromones with 1-ethoxy-1,3,5-tris(trimethylsilyloxy)-1,3,5-hexatriene and its synthetic precursor, ethyl 3,5-bis(trimethylsilyloxy)-2,4-hexadienoate.