Deoxygenation of diols

As vicinal dibromides are usually made by bromination of alkenes, their utility for synthesis is limited, except for temporary masking of a double bond. Much more frequently it is desirable to convert a diol to an alkene, and several useful procedures have been developed. The reductive deoxygenation of diols via thiono carbonates was... 

Schlaf, M., P. Ghosh, P.J. Fagan, E. Hauptman and R.M. Bullock, Metal-Catalyzed Selective Deoxygenation of Diols to Alcohols, Angewandte Chemie International Edition, 40, 3887-3890 (2001). 

Schlaf M, Ghosh P, Fagan PJ, Hauptman E, Bullock RM (2001) Metal-catalyzed selective deoxygenation of diols to alcohols. Angew Chem Int Ed 40 3887-3890... 

B. Reactions in Which Neither Leaving Atom is Hydrogen 17-17 Deoxygenation of Vicinal Diols... 

N-Ethylpiperidi 11 i um hypophosphite has been used as a reductant in deoxygenation of nucleoside diol xanthates in aqueous solution.300... 

A new synthesis of olefins by the reductive deoxygenation of vicinal diols using tungsten(iv) compounds, e.g. K2[WCl6], has been described. The process appears to be the reverse of the reaction of OsO with olefins and to involve transition state (90) since, in corresponding reactions, M0CI4 only forms... 

The A ring is closed by a Ti-mediated reductive coupling (step H-5). The C(ll)-C(12) double bond is introduced from the diol by deoxygenation of the thiocarbonate [step I-... 

Decarbonylation of acyl halides 7-20 Cleavage of Michael adducts 7-21 Deoxygenation of vic-diols 7-22 Cleavage of cyclic thionocarbonates 7-23 Deoxidation of epoxides 7-24 Desulfurization of episulfides 7-25 Reaction of a-halo sulfones with bases (Ramberg-Backlund)... 

Deoxygenation of vie-dials Secondary-tertiary (both cis and tram) vicinal diols are converted into alkenes directly by treatment with chlorotrimethylsilane and sodium iodide in CH3CN at room temperature (80-95% yield, seven examples). 

B. P. Roberts and T. M. Smits, Regioselectivity in the ring opening of 2-phenyl-l,3-dioxan-2-yl radicals derived from cyclic benzylidene acetals and comparison with deoxygenation of a carbohydrate diol via its cyclic thionocarbonate, Tetrahedron Lett., 42 (2001) 3663-3666. 

This reductive coupling involves two steps. The coupling is induced by single electron transfer to the carbonyl groups from alkali metal, followed by deoxygenation of the 1,2-diol with low-valent titanium to yield the alkene. 

The use of organometallic rhenium complexes has found a very broad scope as oxidation catalysts as described in the previous section, making MTO the catalyst of choice for many oxidation reactions of olefins. Interestingly, MTO and related rhenium compounds have also found application in the reverse reaction, the deoxygenation of alcohols and diols. Especially in recent years, this reaction has attracted much attention due to the increased interest in the use of biomass as feedstock for the chemical industry. This section provides an overview of the use of rhenium-based catalysts in the deoxygenation reaction of renewables. 

E. Block, Olefin Synthesis via Deoxygenation of Vicinal Diols, Org. React. 1984, 30, 457-566. 

E. Block, Olefin synthesis via deoxygenation of vicinal diols, Org. React. (N.Y.) 1984, 30, 457. M. M. Midland, Asymmetric reduction with organoborane reagents, Chem. Rev. 1989,89, 1553. H. C. Brown and P. V. Ramachandran, Asymmetric reduction with chiral organoboranes based... 

The Ti(0) then proceeds to deoxygenate the diol by a mechanism not fully understood, but thought to involve binding of the diol to the surface of the Ti(0) particles produced in the reduction ofTiCl3. 

The same polymer-supported organotin reagent was also used in the Barton-type deoxygenation of steroid derivatives, sugar derivatives and diols . Furthermore, the radical deamination of secondary and tertiary amines via the corresponding isocyanides was also reported . 

A variant of this process was used to achieve a chain extension at C5 of a pentose derivative, allowing the construction of the oxahydrinden part of avermectins [59,156]. As shown in Scheme 11.49, the D-ribose derived aldehyde 217 was treated with ( )-trimethylcrotylsilane in the presence of BF3-Et20 [157]. This produced a mixture of three isomers in an 8.9 1.1 1.0 ratio, from which compound 218 was isolated in a yield of 78%. The subsequent steps allowed deoxygenation of the sugar ring to give the diol 219. This compound was, in turn, transformed into the... 

Reductive ozonolysis of the double bond of the appropriate epimer of 36, followed by selective silylation of the diol produced, and radical deoxygenation of the secondary alcohol function, lead to 37, which is a derivative of the cyclohexyl unit of the immunosuppressive agent tacrolimus [20]. 

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