G. Sudhakar Reddy

AN EFFICIENT AND SELECTIVE DEPROTECTION OF ALLYL ETHERS BY A CECL3.7H2O-NAI SYSTEM

Abstract A mild, novel and chemoselective method for the deprotection of allyl ethers by a CeCl 3 .7H 2 O NaI system is described.

Gold(I)-Catalyzed Cyclization for the Synthesis of 8-Hydroxy-3- substituted Isocoumarins: Total Synthesis of Exserolide F

A highly regioselective gold(I)-catalyzed 6-endo-dig cyclization of 2,2-dimethyl-5-(alkynyl)-4H-benzo[d][1,3]dioxin-4-ones for the synthesis of 8-hydroxy-3-substituted isocoumarins is described. Key features of the reaction include the broad substrate scope, scalability, and tolerance for protecting groups. The synthetic utility of this novel method is demonstrated by the first total synthesis of exserolide F, an isocoumarin-containing polyol natural product.

An Efficient and Selective Deprotection of Tetrahydropyranyl Ethers by CeCl3.7H2O

Abstract Treatment of tetrahydropyranyl ethers with cerium (III) chloride heptahydrate in methanol provides a simple, convenient and selective method for detetrahydropyranylation, and the parent alcohols are obtained in high yields.

A NOVEL ONE POT SYNTHESIS OF γ-BUTYROLACTONES*

ABSTRACT α-Arylidene-γ-phenyl-Δβ,γ-butenolides were converted to the respective γ-butyrolactones in methyl alcohol with sodium borohydride in presence of triethylamine in a single pot. *IICT communication No. 4391.

Total Synthesis of Four Isomers of the Proposed Structures of Cryptorigidifoliol K

The first asymmetric convergent total synthesis of four isomers of proposed structures of cryptorigidifoliol K (1a, 1b, 1c, and 1d) has been achieved from commercially available starting materials. The key steps in this synthesis involve tandem isomerization followed by a C-O and C-C bond-forming reaction for the construction of trans-2,6-disubstituted dihydropyran, iodolactonization, isomerization of terminal alkene, and cross-metathesis reaction. The large discrepancies in the spectroscopic data (1H NMR) of synthetic cryptorigidifoliol K from the natural product suggest that the structure of the natural cryptorigidifoliol K requires revision.

A Novel Method for the Regeneration of Alcohols from Toluene Sulphonates Using CeCl3. 7H2O-NaI System

Abstract Treatment of aryl and alkyl tosylates with Cerium(III) chloride hepta hydrate and sodium iodide in acetonitrile provides a simple, convenient and chemoselective procedure for the de tosylation.

CONVERSION OF α-ARYLIDENE-γ-ΚEΤΟ ESTERS TO DIARYLFURAN CARBOXYLIC ACID ESTERS†

Formation of unsymmetrical 2,5 diarylfuran-3-carboxylic acid methyl asters from a-arylidene-7-oxo-benzenebutanoic acid methyl esters in presence of Nbromosuccinimide is described. Introduction Polysubstituted furans have attracted considerable attention due to their presence as key structural units in many of the natural products, important pharmaceuticals, and also as good building blocks in synthetic chemistry. This has led to tremendous interest and demand for flexible synthetic strategies. In general furans are synthesized by the ring closure of suitably substituted 1,4diketones. Alkynyloxiranes, alkynyl allyl alcohols and acetylenic ketones are other wellknown synthons utilized for the synthesis of 2,3,5-trisubstituted furans. Treatment of Grignard reaction product of 3-bromo 2,5-diphenyl furan with carbondioxide and selenium initiated conversions of α-substituted β,γ-unsaturated ketones happen to be few of the known methods reported for the synthesis of 2,5-disubstituted derivatives of furan3-carboxylic acid/ester. During the course of our study on the A-butenolides we came across a novel hitherto observation of forming furans from a-arylidene-y-oxo-benzenebutanoic acid methyl ester IICT Communication No. 01/11/05 Vol. 8, No. 4, 2002 Conversion of a-arylidene-y-keto esters to diarylfuran carboxylic acid esters COOCH3 (II) on treatment with N-bromosuccinimide (NBS) as shown in scheme 1. Ar TM . χΎ NBS/ -> fft 1 Π m Scheme-1 : Formation of furan derivatives with NBS Compound II, can be obtained in quantitative yield from the respective A-butenolides (I) by treatment with triethylamine in methyl alcohol at room temperature, the reaction time being 1 to 4 h. Results and Discussion We envisaged the bromination of the active methylene of compound II with NBS, to extend it further for the synthesis of heterocycles, but instead resulted in the formation of 2-aryl 5-phenylfuran-3-carboxylic acid methyl esters (III) In a typical reaction a-arylidene-7-oxo-benzenebutanoic acid methyl ester was treated with equimolar quantities of N-bromosuccinimide in refluxing carbon tetrachloride. Unsymmetrical diaryl substituted furan-3-carboxylic acid esters (III) were obtained in good yields. All the products obtained were characterized on the basis of IR, NMR, Mass spectra and HRMS. The Table-1 depicts the results of the present investigation. Table-1 : Effect of substitution in product formation Entry Ar Product Yield (%) Melting Point (°C) 1. 4-OCH3CeH4 95 78 2. 4-CH3CeH4 80 101 3. 4-OHCeH4 50 124 4. 4-OH-3-OCH3CeH3 80 72 5. CeH5 No reaction 6. 4-N02CeH4 No reaction 7. 2,6-Cl2CeH3 No reaction 8. 3-OPhCeH4 No reaction