Sengodagounder Muthusamy

Tandem cyclization–cycloaddition reactions of rhodium generated carbenoids from α-diazo carbonyl compounds

The rapid generation of molecular complexity, in a controlled and predictable manner, is a contemporary theme in the practice of modern organic synthesis and finds application in accessing newer entities for the pharmaceutical industry. Efficiency, atom economy, regio-, stereo- and enantiocontrol, ready availability of starting materials and environmentally benign processing are some of the common concerns in any synthetic endeavor. Synthetic brevity is, however, central to the generation of molecular complexity in a resource-effective manner and, in order to attain that objective, two strategic options have been generally explored in recent years, one involving multicomponent reactions and the other involving reactions leading to multiple carbon-carbon bond formation through tandem processes. The latter approach involves recourse to reactions like multiple cycloadditions or cyclization–cycloaddition sequences in which many bonds are formed in a single mode operation and these cascade processes have an inherent advantage in expeditiously assembling polycyclic structures with proper stereochemical control.

Indium(III) chloride as an efficient, convenient catalyst for thioacetalization and its chemoselectivity

An efficient method for the preparation of 1,3-dithiolanes from aldehydes and ketones with 1,2-ethanedithiol in the presence of a catalytic amount of anhydrous indium(III) chloride is reported. A mild and highly chemoselective thioacetalization of carbonyl compounds using indium(III) chloride as the catalyst is also described. The desired products were obtained in 71–95% yield.

Indium triflate: a mild Lewis acid catalyst for thioacetalization and transthioacetalization

Abstract Protection of a variety of carbonyl compounds as thioacetals using indium triflate, a mild Lewis acid catalyst, was achieved at ambient temperature in very good yield. Transthioacetalization of oxyacetals into thioacetals was also achieved in an excellent yield. A mixture of carbonyl compound and its respective oxyacetal was also completely converted into thioacetal in the presence of indium triflate.

Facile Synthesis of Oxatricyclic Systems with Various Ring Sizes and Substituents

Abstract A series of α-diazo carbonyl compounds having cyclopentanone, cyclohexanone and substituted cyclohexanone units with different tether lengths have been synthesized using diazomethane solution or methanesulphonyl azide. The above synthesized α-diazo carbonyl compounds with rhodium(II) acetate dimer furnish cyclic five- or six-ring carbonyl ylide dipoles, which undergo facile 1,3-dipolar cycloaddition with different dipolarophiles to furnish the substituted and functionalized oxatricyclic systems having various ring sizes. Two X-ray crystallographic analyses of compounds 8b and 15a are reported to firmly establish the stereochemistry of the cycloadducts.

Novel regioselective synthesis of decahydrobenzocarbazoles using rhodium generated carbonyl ylides with indoles

Abstract Intermolecular cycloadditions of five-membered cyclic carbonyl ylides 3 with indole, N -methylindole and N -benzylindole afforded decahydrobenzo[ c ]carbazole 4a–f or decahydrocyclopenta[ c ]carbazole 4g–h derivatives with high regioselectivity. With N -benzoylindole and N -sulphonylindole, decahydrobenzo[ c ]carbazoles 4i,j and the regioisomer decahydrobenzo[ a ]carbazoles 5i,j are isolated. The electron withdrawing substituent reduces both regioselectivity and reactivity of the cycloadditions. This methodology generated oxa-bridged (unnatural) decahydrobenzocarbazole derivatives with complete control of four stereocenters.

Indium triflate: a mild and efficient Lewis acid catalyst for O–H insertion reactions of α-diazo ketones

Abstract Facile O–H insertion reactions of α-diazo ketones with aliphatic/aromatic alcohols or benzenethiol have been developed in the presence of indium triflate as a catalyst. These reactions provided good yields of α-alkoxy ketones. A comparative study with other Lewis acids establishes the reactivity of indium triflate in O–H insertion reactions of α-diazo ketones.

Atom-Economical Access to Highly Substituted Indenes and Furan-2-ones via Tandem Reaction of Diazo Compounds and Propargyl Alcohols

A facile synthesis of highly substituted as well as conjugated indene/furanone systems via a BF3·OEt2 catalyzed tandem reaction of α-diazo-esters/-amides and propargyl alcohols has been demonstrated under mild conditions. This method offers great potential for the synthesis of biologically active indene and furanone derivatives and their related polycyclic compounds.

Novel chemoselective 1,3-dipolar cycloaddition of rhodium generated carbonyl ylides with arylidenetetralones

Abstract Treatment of various α-diazo ketones 1 and arylidenetetralones 2 in the presence of rhodium(II) acetate dimer leads to spiro-dioxa ring systems 3 as the only CO addition products with high regio- and chemoselectivity.

Rhodium generated carbonyl ylides with p-quinones: synthesis of oxa-bridged polycyclic systems

Abstract A series of α-diazo carbonyl compounds tethered to substituted cyclopentanone and cyclohexanone units with different tether lengths have been synthesized using diazomethane solution or methanesulphonyl azide. The above synthesized α-diazo carbonyl compounds with rhodium(II) acetate dimer furnish cyclic five- or six-membered-ring carbonyl ylide dipoles, which undergo facile 1,3-dipolar cycloaddition with p-quinones to furnish various novel oxa-bridged polycyclic systems 10, 13 and 11, 14 as C C and C O addition products of p-quinones. Very interesting unusual cyclization product, tri-oxapolycyclic compounds 12 and 15 were also obtained. Single-crystal X-ray analyses of 11a, 12d and 14a are reported to firmly establish the structure and stereochemistry of the oxa-bridged polycyclic systems. The molecules 11a and 14a exhibit novel C–H⋯O hydrogen bonding motif in the crystal structure. On the other hand, the molecule 12d revealed both O–H⋯O and C–H⋯O motifs in the solid-state architecture.

Anomalous behaviour of Rh(II)-generated carbonyl ylides: entry into functionalized spiro dioxa-bridged polycyclic frameworks

Abstract A series of symmetrical α,β-unsaturated ketone systems having multiple π-bonds were synthesized. To generate five-membered-ring carbonyl ylides as intermediates, the rhodium(II)-catalyzed reactions of α-diazo ketones were carried out and the carbonyl ylides reacted with the π-bonded α,β-unsaturated ketone systems. Functionalized spiro dioxa-bridged polycyclic ring systems were produced with high regio- and chemoselectivity in good yields.