Amitabha Sarkar

Effect of a proximal oxygen substituent on the efficacy of ruthenium-catalyzed cross-metathesis and RCM

Ruthenium-catalyzed cross-metathesis of various derivatives of 1,2-dihydroxy-3-butene reveals that cyclic acetals are best suited as substrates compared to acyclic diethers or diacetates, while RCM is relatively insensitive to the presence of allylic or homoallylic hydroxy or acetoxy groups.

Highly diastereoselective Michael addition to 2-arylidene-1-tetralones complexed with Cr(CO)3+

Abstract Conjugate addition of nitromethane to 2-arylidene-1-tetralones anchored on Cr(CO) 3 was found to be about 100% stereoselective.

Assembling monocyclic, spirocyclic and fused carbocycles by ring-closing metathesis on an arene–chromium template

Abstract A variety of diene precursors assembled stereoselectively on an arene–chromium template underwent facile ring-closing metathesis by ruthenium catalysis at ambient temperature to afford cyclic compounds of varying degrees of complexity in high yields.

Alkali metal hydride or aqueous hydroxide induced conjugate addition of trimethylsilyl enol ethers to enones. A convenient alternative to Lewis acid mediated reaction

Abstract Conjugate addition to enones by enolates derived from base-induced cleavage of OSi bond of trimethylsilyl enol ethers, yields 1,5-dicarbonyl compounds in good yields.

SYNTHESIS OF NEW STEREOCHEMICALLY NON-RIGID MOLYBDENUM-ALLYL COMPLEXES CONTAINING THE BIS(3,5-DIMETHYLPYRAZOLYL)METHANE LIGAND

A convenient preparation of LMo(CO)4 (L = bis(3,5-dimethylpyrazolyl)methane) and the syntheses of several fluxional cis-LMo(CO)2(allyl) compounds are reported. Their proton NMR spectra are discussed.

Isolation and characterization of [Fe2(CO)6Se2{μ-(CO)3Cr(η5-C5(H)(CH2Ph)(Ph)(OEt)}], [(CO)6Fe2{μ-EC(Ph)=C(E′)C(H)(OEt)}]2 and [(CO)6Fe2{μ-SC(H)(Ph)C(Te)=C(H)(OEt)}] from the thermolysis of Fischer carbene adducts [(CO)6Fe2EE′{μ-C(Ph)=C–C(OEt)=Cr(CO)5}] (E,E′=Se and E=S, E′=Te)

Abstract Thermolysis of the trimetallic adducts [(CO)6Fe2EE′{μ-C(Ph)C–C(OEt)Cr(CO)5}] 1a,b (1a: E=E′=Se; 1b: E=S, E′=Te) in refluxing THF yield the following complexes: [Fe2(CO)6EE′{μ-(CO)3Cr(η5-C5(H)(CH2Ph)(Ph)(OEt)}], (2: E=E′=Se); [(CO)6Fe2{μ-EC(Ph)C(E′)C(H)(OEt)}]2, (3a: E=E′=Se; 3b: E=S, E′=Te) and [(CO)6Fe2{μ-EC(H)(Ph)C(E′)C(H)(OEt)}], (4: E=S, E′=Te), where the product formation depends on the nature of chalcogen atoms present in the trimetallic adducts 1a and 1b. All products have been characterized by IR and 1H-, 13C-, 77Se- and 125Te-NMR spectroscopy and structural types were unequivocally established by X-ray crystallographic analysis of compounds 3a and 4.

Synthesis and structure of novel, air-stable carbyne complexes of tungsten

Abstract New Fischer type carbyne complexes of tungsten, L(CO)2WCR/Ar, 1b–7b, where R=CH3, Ar=substituted phenyl, and LH=(2-hydroxyphenyl)-bis(3,5-dimethylpyrazolyl)methane, with L− being a tridentate, uninegative ligand, were synthesized from W(CO)6 via tetraethylammonium acylmetallate salt, as thermally stable and air-stable solids. In another complex, 8b, the aryl ring is complexed with tricarbonylchromium. Crystal structure of a representative complex was determined to confirm structural assignment.

Excellent diastereoselectivity in triflate-catalyzed addition of acyclic enolsilanes to η6-(ortho-substituted-benzaldehyde)-Cr(CO)3 complexes

Abstract Scandium, rare earth or trimethylsilyl triflate catalyzes highly diastereoselective addition of silyl enol ethers to chiral benzaldehyde-Cr(CO)3 complexes at ambient temperature.

MgBr2-directed endo-selective conjugate addition of organometallic reagents to enones anchored on Cr(CO)3

Abstract Addition of RMgX or RLi/MgBr 2 to 2-arylidene-1-tetraloneCr(CO) 3 complexes takes place in a conjugate manner with complete endo selectivity.

Chelation-control in nucleophilic addition to Cr(CO)3-complexed aryl aldehydes

One or more methoxy groups on the benzylic carbon at the ortho-position of tricarbonylchromium-complexed aryl aldehydes (2, 3 or 4) permit chelation-controlled addition of nucleophiles to the carbonyl function in the presence of Lewis acids. In the absence of a Lewis acid additive, a complementary set of diastereomeric products are obtained.