Angshuman Chattopadhyay

[bmim][Br] as a Solvent and Activator for the Ga-Mediated Barbier Allylation: Direct Formation of an N-Heterocyclic Carbene from Ga Metal

The room-temperature ionic liquid (RTIL) [bmim][Br] has been found to be an excellent green and inexpensive medium for the Ga-mediated allylation of aromatic and aliphatic aldehydes and ketones. The RTIL activated the metal via formation of a Ga-N-heterocyclic carbene complex that assisted in the completion of the reaction at ambient temperature with only 0.5 equiv of Ga and 1.2 equiv of allyl bromide with respect to the carbonyl substrates. The present protocol required a much shorter time than those reported in the literature using other metals and solvents and proceeded with good yields and excellent selectivity.

Facile approach towards the synthesis of homochiral functionalised alcohols from 4-O-[(tert)-butyldimethylsilyl]-2,3-O-cyclohexylidene-l-threose of (l)-(+)-tartaric acid origin

Abstract ( l )-(+)-Diethyl tartarate 2 has been transformed into the aldehyde 6 . Grignard additions to 6 take place with moderate diastereoselectivity giving predominant formation of the anti products 8a – e . However, in each case the diastereoalcohols are easily separable by column chromatography giving rise to the formation of a series of functionalised homochiral alcohols 7 and 8 . On the other hand Zn mediated allylation and propargylation of 6 in the presence of water proceeded efficiently with almost absolute (>99%) stereoselective formation of versatile functionalised homoallylic 8d and homopropargylic 8e alcohols respectively.

(R)-2,3-Cyclohexylideneglyceraldehyde: A versatile intermediate for sugar modified dideoxynucleosides

Abstract ( R )-2,3-Cyclohexylideneglyceraldeyde 1 has been found to be a useful intermediate for the convenient synthesis of both threo- and erythro- forms of functionally rich 2-deoxypentofuranoses, possible precursors of sugar modified 2′,3′-dideoxynucleosides. This has been exemplified by the exploitation of its major allylation product 2b for a short synthesis of 4 and 8 and subsequent transformation of 8 to threo 3-azido-2,3-dideoxypentofuranose 9 .

Stereoselective Synthesis of Methyl Branched Eicosa-5(Z), 9(Z)-dienoic Acids, Components of the Sponge, Erylus formosus

Abstract A stereoselective synthesis of two marine fatty acids viz. 19-methyleicosa-5(Z), 9(Z)-dienoic acid (I) and 18-methyleicosa-5(Z), 9(Z)-dienoic acid (II) has been developed. The synthetic strategy was based on C‒C bond formation via (Z)-selective Wittig olefination of the required synthons which in turn were prepared from readily available materials.

Stereoselective Synthesis of 7-Methylhexadec-6-enoic Acid, a Component of Carribean Sponge

Abstract The marine natural product (E)-7-methyl hexadec-6-enoic acid(I), has been synthesised for the first time starting from commercially available methyl vinyl ketone. Stereoselective generation of its tri- substituted olefinic moiety is accomplished via Claisen orthoester rearrangement.

Synthesis of the Demospongic Compounds, (6Z, 11Z)-Octadecadienoic Acid and (6Z, 11Z)-Eicosadienoic Acid

B. A. Kulkarni, S. Chattopadhyay*, A. Chattopadhyay and V. R. MamdapurBio-Organic Division, Bhabha Atomic Research Centre, Mumbai - 400 085, India. Tel. 91-22-5563060; Fax 91-22-5560750 (bod@magnum.barct1.ernet.in)Received: 20 December 1996 / Accepted: 10 January 1997 / Published: 29 January 1997Abstract: A stereoselective synthesis of (6 Z , 11Z )-octadecadienoic acid ( 1) and (6 Z , 11Z )-eicosadienoic acid ( 2)from easily accessible pentane-1,5-diol ( 3) is described. Thus, compound 3 on pyranylation and oxidation gavethe aldehyde 5 which was converted to the acid 7 by Wittig reaction with a suitable phosphorane. Its depyranylationand oxidation furnished the key aldehyde 9 which upon Wittig reaction with n-heptylidene and n-nonylidenephosphoranes, respectively followed by alkaline hydrolysis afforded the title acids.Keywords : Euryspongia rosea , phospholipid fatty acids, stereoselective synthesis, (6 Z , 11 Z )-octadecadienoicacids, (6 Z , 11 Z )-eicosadienoic acids, Wittig olefination.IntroductionThe marine environment [1] constitutes an exhaustible treas-ury of organisms generating a plethora of secondarymetabolites. In this regard, sponges, the primitive multicel-lular organisms have recently been the targets [2] of lipidchemistry not only for the product fatty acids but also due totheir biosyntheses. It is now believed that a combination ofde novo biosynthesis, dietary intake, and incorporation ofmicroorganic symbionts are responsible for the genesis ofthese varied types of novel fatty acids in sponges. Besidesthe presence of very long chain fatty acids, sponges haveprovided fatty acids with unusual unsaturation patterns, sub-stitutions with oxygenated functionalities (hydroxy, methoxy,acetoxy) and methyl branching.Recently, from the marine sponge, Euryspongia rosea ,two such compounds viz. (6Z , 11Z )-octadecadienoic acid ( 1)and (6 Z , 11 Z )-eicosadienoic acid ( 2) have been isolated [3]from the phospholipid fraction. This type of ∆

A facile and simple entry into isodideoxynucleosides

Sharpless asymmetric dihydroxylations of homoallylic alcohol derivative 3 with AD mix-α afforded α addition product 4a predominantly. Compound 4a was produced with very high selectivity when 3 was treated with AD mix-β. The inherent hydroxylic functionalities of 4a were judiciously exploited to develop a simple and efficient synthesis of (3′S,5′S)-isodideoxynucleosides. I and II are two representative target molecules for our synthesis in this regard.