Olefin Synthesis by Deoxygenation of Vicinal Diols

Abstract

Since the discovery in 1963 that 1,3‐dioxolane‐2‐thiones (cyclic thionocarbonates) undergo stereospecific fragmentation to olefins on heating with trivalent phosphorus compounds (the Corey–Winter reaction), a variety of approaches have been developed for the regio‐ and stereospecific (or stereo‐selective) deoxygenation of vicinal diols based on syn elimination from cyclic derivatives. These methods have been particularly useful in synthesizing substrates with delicate structural features such as strained and twisted olefins, unsaturated carbohydrates, macrocyclic lactones, lipids, and polyenes, as well as in establishing the stereochemistry of diol functions in natural products. This chapter deals primarily with deoxygenation of vicinal diols via cyclic species with X = C, P, Ti, W, or S (suitably functionalized). Brief coverage is given to deoxygenation processes that do not involve cyclic intermediates, whereas routes proceeding via oxiranes or vic ‐dihalides as separately isolated intermediates are excluded from consideration. The stereochemical equilibration of vicinal diols and the conversion of vicinal hydroxy thiols and dithiols to olefins are also covered in this chapter. Brief reviews have appeared in the literature of the Corey–Winter reaction and of the general topic of deoxygenation of vicinal diols.

Triphenylphosphine-2,4,5-Triiodoimidazole

“…Methods for the conversion of vicinal diols to alkenes have found significant utility in organic synthesis and a number of nonphosphine-based methods have also been developed. 11 Treatment of methyl 2,6-dibenzyl-α-D-glucopyranoside with triphenylphosphine-2,4,5-triiodoimidazole in a 2:1 excess over the substrate affords the unsaturated sugar in a reported 95% yield (eq 1). Samuelsson 1 and others 13 report that the reagent works best in the case of trans-diequatorial or trans-diaxial diols; however, Ozaki and co-workers 14 used the reagent effectively on a mixture of cis-and trans-diols.…”

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

“…Treatment of the nucleosides 2 provide an effective synthetic route to 2',3'-unsaturated nucleosides 3 (see Scheme 2 and Table 1). Today a number of methods offer olefins from vicinal diols [39,40]. 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].…”

Triethyl Orthoformate

“…15, 16 Those orthoformates obtained from 1,2-diols (eq 4) 3 can undergo cycloelimination upon pyrolysis to afford alkenes in high yield. 17 There are a variety of methods for carrying out this overall process, 18 (4) Acetals and Enol Ethers. The conversion of the orthoformate to formate is energetically favored.…”