Carlos Alvarez-Ibarra

SYNTHESIS OF POLYSUBSTITUTED 3-THIOFURANS BY REGIOSPECIFIC MONO-IPSO-SUBSTITUTION AND ORTHO-METALLATION FROM 3,4-DIBROMOFURAN

The synthetic potential of 3,4-dibromofuran has been assessed by its conversion into 3,4-disubstituted furans via mono-S-ipso-substitution. The ability of 3-methylthio and 3-phenylthio substituents for directing the metallation at position α-relative to the substituent has allowed the regiospecific alkylation. It provides a straightforward approach to several 3-monothiosubstituted furans which are receiving increasing interest as odour and flavour chemicals.

Carboxylates as pronucleophiles in the phosphine-catalyzed γ-addition reaction

Abstract Carboxylates have been used as pronucleophiles in the phosphine-catalyzed γ-addition reaction to alkynes bearing electron-withdrawing groups (Trosts reaction) giving rise to functionalized allyl carboxylates.

An efficient and stereoselective Wittig-Horner synthesis of acyclic α-enones with barium hydroxide as solid catalyst

Wittig–Horner reactions under interfacial solid–liquid conditions using activated barium hydroxide catalyst C-200 produce acyclic α-enones with high yields and selectivities.

Diastereoselective synthesis of 4-substituted 5-(p-tolylsulfinyl)-5,6-dehydropiperidin-2-ones. A new approach to methyl L-(2S, 4S)-4-methyl-6-oxopipecolate

Abstract The sulfoxide-mediated diastereoselective Michael reaction of homochiral α-sulfinylketimines 1a – d and β-substituted ene esters 2a – d (Huas reaction) was explored. Straightforward cyclization of the open-chain adducts take place under the reaction conditions to provide the 4-substituted 5-( p -tolylsulfinyl)-5,6-dehydropiperidin-2-ones 3 and 7 – 12 , whose stereochemistry is formed in the prior step. Furthermore, the role of the metal ion of the aza-enolate reagents and the steric demands of the O -alkyl ester group have been examined. It seems that the anti -diastereoselectivity depends on metal chelation by the oxygen of the ester as well as the oxygen of the sulfinyl group and the nitrogen in the aza-enolate (( Z )-configuration). In addition, the synthesis of methyl l -(2 S ,4 S )-4-methyl-6-oxopipecolate has been achieved from the suitably functionalized 2-sulfinylketimine 1a (five steps; overall yield: 53–65%).

Conformationally restricted glutamic acid derivatives: asymmetric synthesis of 4-substituted 4,5-dihydro-3(2H)-pyridazinones

Abstract The synthesis of optically pure 4,5-dihydro-3(2 H )-pyridazinones substituted at C-4, which can be considered conformationally restricted cyclic Glu derivatives, has been accomplished by the asymmetric γ-alkylation of α,β-unsaturated glutamyl sultams under PTC conditions followed by reaction with hydrazines.

Stereoselective cyanosilylation of α-sulfinylketimines or its covalently stabilized enamine tautomers. Synthesis of enantiomerically pure α-sulfinylmethyl-α-amino nitriles

Abstract α-Sulfinylketimines and β-sulfinylenamines undergo reaction with delivery cyanide reagents such as TMSCN or TBDMSCN in the presence of either stoichiometric excesses of ZnCl 2 or ZnBr 2 , or catalytic amount of Yb(TfO) 3 . The use of ZnCl 2 in alcohol solvents provides the best diastereoselectivity. It is mediated by a chelated transition state, the p -tolyl group driving the anti attack of the reagent. By using Yb(TfO) 3 poor diastereoselectivities but good yields are obtained. It seems that an iminium derivative originated by metal coordination with either the nitrogen or oxygen atom in the substrate is responsible for the observed results. Interestingly, β-sulfinylenamines provide analogous α-amino nitriles in the same reaction conditions. It allowed the cyanosilylation of the covalently stabilized enamines arising from unstable β-sulfinyl aldehydes.

A novel synthesis of thiazoles from dimethyl N-(ethoxycarbonylmethyl)imino dithiocarbonate, carbon disulfide and alkyl halides

Abstract We report a new synthesis of thiazoles from a cyclocondensation reaction between dimethyl N-(ethoxycarbonylmethyl)iminodithiocarbonate (EMIC), carbon disulfide and alkylation of intermediate thiazole-2-thiolate with alkyl halides.

Reaction of N-[bis(methylthio)methylene]glycinates with electron deficient alkynes. Synthesis of (Z)-α,β-didehydroglutamic acid derivatives

Abstract The addition of either the alkaline enolates of the glycinates 1 or their naked enolates to electron defficient alkynes allows for the synthesis of substituted ( Z )- α , β -didehydroglutamic acid derivatives 7 via a Michael addition /1,3-prototropic rearrangement sequence.

Sulfoxide-mediated diastereoselective Michael additions. New enantioselective synthesis of C-4 substituted 2-pyroaminoadipic acids

Abstract Diastereoselective reactions of suitably functionalized homochiral β-iminosulfoxides with Michael acceptors provide a new and efficient route for the asymmetric synthesis of C-4 substituted 2-pyroaminoadipates. Extension of the scope of the sulfoxide-mediated aza-enolate conjugate addition (Huas reaction) has also been explored.

A new synthetic approximation to thiazoles with a versatile persubstitution and/or perfunctionalization

A new synthetic approach to 2-alkyl-, 2-aryl-, and 2-N-alkylaminothiazoles has been carried out. This strategy is based on the high versatility of synthons derived from 2-methylthiothiazoles