Reactions of relevance to the chemistry of aminoglycoside antibiotics. Part 11. Preparation of olefins from vicinal diols

Abstract

Vicinal diols are converted in high yield into olefins by reaction of the derived bisdithiocarbonates with tri-n-butylstannane in toluene or benzene. The stereochemistry of reaction is consistent with a stepwise radical fragmentation. College, London SW7 2AYRECENTLY, carbohydrate esters containing the thiocarbonyl group have found application in novel mild procedures whereby hydroxy-functions may be selec-tively replaced by hydrogen or halide~.~93 For example, the reaction of 0-alkyl-S-methyldithiocarbonates (xanthates) with methyl iodide gave the iodoalkane and di-S-reduction of xanthates with tri-n-butylstannane gave the deoxy-compound via a radical fragmentation (Scheme 1). Substitution in the P-position of the intermediate alkyl radical by a good radical leaving group should permit the synthesis of alkenes. Herein is described the conversion of vicinal diols into alkenes by the radical fragmentation of the derived bis-xantliates (Scheme Attempts to prepare bisthioxobenzoates from vicinal diols using the Vilsmeier reagent (Me,&=CClPhd) were unsuccessful due t o formation of 1,2-chlorobenzoates via the cation (1) (Scheme 3).5 Since the preparation of xanthates proceeds via anionic intermediates, species analogous with the cation (1) cannot be formed. Consistent with this and literature p r e~e d e n t ,~.~ a series of carbohydrate diols (2a), (3a), (5a), and (7a) were converted into the bis-xanthates (2b), (3b), (5b), and (7b), respectively, using sodium hydride (catalysed by imidazole), carbon disulphide, and methyl iodide in sequence in tetrahydrofuran (THF), as detailed previously for monoxanthates. Formation of the bisxanthates was consistent with spectra and. microana-2) .4 RHR + Bunj Sn' _____) R R\ / I Bun3SnSCOSMe SCHEME 2 methyldithiocarbonate via S-methylation followed by SN2 displacement by iodide anion. Alternatively, properties in agreement with literature values.6 and S.

D-Arbinose-Based Synthesis of homo-C-d4T and homo-C-thymidine

“…Selective tritylation of the primary -OH group in this triol furnished a crystalline derivative 41 which was converted to the olefin 42 via Bu 3 SnH/AIBN reduction of its bis-thiocarbonyl ester. [111,112] Removal of the -TBDMS group (Bu 4 NF) furnished the unsaturated alcohol 43. It should be pointed out that 43 in its deprotected form 44 has a plane of symmetry, therefore both hydroxymethyl groups are enantiotopic.…”

Photoinduced electron-transfer α-deoxygenation of aldonolactones. Efficient synthesis of 2-deoxy-d-arabino-hexono-1,4-lactone

“…This feature of the PET reaction is not shared by the BartonMcCombie deoxygenation, by which a bis-xanthate would give a C-2-C-3 olefin. 19 The identity of compounds 9, 10, 13, 14, and 16 was established on the basis of their NMR spectra. The presence of two doublets of doublets at high fields (d 3.00 and 2.50, Table 1), with a large J gem ($18.0 Hz) in the 1 H NMR spectra, and the signal corresponding to the deoxy function (C-2) at $39.0 ppm in the 13 C NMR spectra ( In conclusion, the PET deoxygenation reaction on aldonolactones that are conveniently derivatized allows selective deoxygenation at C-2.…”

Synthesis of 2,3-Didehydro-2,3-dideoxynucleosides via Nucleoside Route.

“…Olefins can be obtained directly from vicinal diols by treatment with titanium metal [41,42], Me 3 SiCl-NaI [43], Ph 3 P-I 2 -imidazole [44], Ph 2 PCl-I 2 -imidazole [45], PBr 3 -CuBr-Zn [46] or tungsten reagent such as K 2 WCl 6 [47]. However the main methods require the introduction of activating groups: (i) vicinal bromoacetate [48]; (ii) cyclic thionocarbonate [49,50]; (iii) 1,3-dioxolane [51][52][53][54]; (iv) vicinal dixanthates [55][56][57][58]; (v) vicinal disulfates [59,60]; (vi) cyclic phosphates [61][62][63]; (vii) phosphoramidate [61][62][63]; (viii) cyclic sulfate [64][65][66][67][68]. Few of the known methods for conversion of vicinal diols to olefins have been applied to ribonucleosides.…”