Rosa López

Phosphazene bases for the preparation of biaryl thioethers from aryl iodides and arenethiols

In the presence of phosphazene P2-Et base as well as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) the coupling of aryl iodides with arenethiols only requires catalytic amounts of CuBr. Under these conditions the reaction can be performed in refluxing toluene to give biaryl thioethers in excellent yields.

Asymmetric aza-Henry reaction under phase transfer catalysis: an experimental and theoretical study.

An efficient catalytic asymmetric aza-Henry reaction under phase transfer conditions is presented. The method is based on the reaction of the respective nitroalkane with alpha-amido sulfones effected by CsOH x H2O base in toluene as solvent and in the presence of cinchone-derived ammonium catalysts. This direct aza-Henry reaction presents as interesting features its validity for both nonenolizable and enolizable aldehyde-derived azomethines and the tolerance of nitroalkanes, other than nitromethane, for the production of beta-nitroamines. The synthetic value of the methodology described is demonstrated by providing (a) a direct route for the asymmetric synthesis of differently substituted 1,2-diamines and (b) a new asymmetric synthesis of gamma-amino alpha,beta-unsaturated esters through a catalytic, highly enantioselective formal addition of functionalized alkenyl groups to azomethines. Finally, a preferred TS that nicely fits the observed enantioselectivity has been identified. Most remarkable, an unusual hydrogen bond pattern for the catalyst-nitrocompound-imine complex is predicted, where the catalyst OH group interacts with the NO2 group of the nitrocompound.

Cyanoalkylation: Alkylnitriles in Catalytic CC Bond‐Forming Reactions

Alkylnitriles are one of the most ubiquitous nitrogen-containing chemicals and are widely employed in reactions which result in nitrile-group conversion into other functionalities. Nevertheless, their use as carbon pronucleophiles in carbon-carbon bond-forming reactions has been hampered by difficulties associated mainly with the catalytic generation of active species, that is, α-cyano carbanions or metalated nitriles. Recent investigations have addressed this challenge and have resulted in different modes of alkylnitrile activation. This review illustrates these findings, which have set the foundation for the development of practical and conceptually new catalytic, direct cyanoalkylation methodologies.

Catalytic enantioselective Mannich-type reaction with beta-phenyl sulfonyl acetonitrile.

The organocatalytic addition of beta-phenyl sulfonyl acetonitrile 1 to either N-Boc-protected alpha-amido sulfones or imines allowed the synthesis of enantioenriched alpha-unsubstituted beta-amino nitriles through a Mannich-type reaction.

A mild, convenient, and inexpensive method for converting imines into amines: Tin-catalyzed reduction with polymethylhydrosiloxane (PMHS)

Abstract We have developed a mild, convenient, and inexpensive protocol for reducing imines to amines. Thus, treatment of any of a wide array of imines with catalytic n -butyltris(2-ethylhexanoate)tin and stoichioimetric polymethylhydrosiloxane (PMHS) in ethanol at room temperature cleanly affords the desired secondary amine product. Alkyl bromides, alkynes, epoxides, esters, nitriles, and olefins are inert toward these reduction conditions, whereas aldehydes, ketones, and nitro compounds are not.

Catalytic Enantioselective Synthesis of Tertiary Thiols From 5H‐Thiazol‐4‐ones and Nitroolefins: Bifunctional Ureidopeptide‐Based Brønsted Base Catalysis

reactions of a-sulfanyl lactones.Accordingly, whilst many methodologies for the enantiose-lective synthesis of secondary thiols exist, approaches for theasymmetric synthesisoftertiarythiolsareclearlynecessarytohelp fill this important gap in organic chemistry. The inherentdifficulty associated with the stereoselective construction ofquaternary stereogenic centers is probably the reason for thelimited number of studies.

Ureidopeptide-based Brønsted bases: design, synthesis and application to the catalytic enantioselective synthesis of β-amino nitriles from (arylsulfonyl)acetonitriles.

The addition of cyanoalkyl moieties to imines is a very attractive method for the preparation of β-amino nitriles. We present a highly efficient organocatalytic methodology for the stereoselective synthesis of β-amino nitriles, in which the key to success is the use of ureidopeptide-based Brønsted base catalysts in combination with (arylsulfonyl)acetonitriles as synthetic equivalents of the acetonitrile anion. The method gives access to a variety of β-amino nitriles with good yields and excellent enantioselectivities, and broadens the stereoselective Mannich-type methodologies available for their synthesis.

Catalytic asymmetric synthesis of γ-substituted vinyl sulfones.

A fast new entry for the stereoselective construction of γ-substituted vinyl sulfones is presented. The key for success is the use of a readily available chiral secondary amine catalyst that allows the use of base-sensitive β-nitroethyl sulfones as masked β-sulfonyl vinyl anions in conjugate additions. The method performed in a three-step one-pot operation gives access to a great variety of vinyl sulfones in good yields and with excellent enantioselectivities. The method has also been extended to other relatively base-sensitive β-electron-withdrawing-substituted nitroalkanes to afford products with manifold functionality, providing a quick entry to very attractive synthetic intermediates for organic synthesis.

Base-Catalyzed Asymmetric α-Functionalization of 2-(Cyanomethyl)azaarene N-Oxides Leading to Quaternary Stereocenters

A simple, new strategy for the direct asymmetric α-functionalization of 2-alkyl azaarenes is described. Specifically, a Brønsted base catalyzed conjugate addition of substituted 2-cyanomethylpyridine (and pyrazine) N-oxides to acrylate equivalents to afford hitherto elusive 2-tert-alkyl azaaryl adducts with high enantioselectivity (up to 94% ee) is realized. Extension of the method to the α-amination reaction by using azodicarboxylate esters as electrophiles is also demonstrated. Key for success is the N-oxide functionality of substrates that acts as a removable activating and stereodirecting group. A bifunctional Brønsted base catalyst bearing a squaramide with an attached bulky silyl group is also disclosed.

Phosphazene P4-But base for the Ullmann biaryl ether synthesis

In the presence of phosphazene P4-But base and CuBr, aryl halides couple with phenols to give biaryl ethers at ca. 100 °C