Direct deoxygenation

Yamashita, M., Tsunekawa, K., Sugiura, M., and Oshikawa, T., Novel preparation of diphenylphosphine oxides via direct deoxygenation of 1,2-epoxy-ethyldiphenylphosphine oxides, Synthesis, 65, 1985. 

The utility of the method depends on the availability of the dioxime precursors. When the parent quinone is readily accessible, direct oximation provides a straightforward approach which has been used for the acenaphtho- and phenanthro-furazans, (22) and (94 n= 0), although in the former case mild conditions (SOCl2, 20 °C) are required for the subsequent cyclodehydration in order to avoid fragmentation of the product (73JOC1054) (see Section 4.22.3.1.1). o-Quinone dioximes can be generated by reduction of benzo-furoxans, but in many such cases direct deoxygenation to the benzofurazan is also possible. 

Tervalent phosphorus has a high affinity for oxygen and the P=0 bond once formed is very strong. This fact, which also provides the driving force for the Wittig and related reactions, has led to the widespread use of P(III) compounds for direct deoxygenation of epoxides, ozonides, carbonyl compounds, and both N- and 5-oxides.2... 

The direct deoxygenation of ketones via the Clemmensen reduction requires strong acidic conditions and high temperatures hence it is not suitable for acid-sensitive compounds. 

Sharpless, K. B., Flood, T. C. Direct deoxygenation of vicinal diols with tungsten(IV). New olefin synthesis. J. Chem. Soc., Chem. Common. 1972,370-371. 

Alkanes. The phosphonium salt (from PhjPO + Tf20) activates alcohols for direct deoxygenation with NaBH4. 

Raney Ni has been successfully employed for the direct deoxygenation of tertiary alcohols to alkanes (equation 15). Under the reaction conditions other sensitive functionalities like t-butyldimethylsilyl ethers, acetates and alkyl chlorides are stable. ... 

Tertiary alcohols are seldom amenable to direct deoxygenation. However, sodium cyanoborohydride in the presence of zinc iodide reduces tertiary alcohols to the corresponding alkanes in high yields. Primary and secondary alcohols are not reduced with this reduction reagent and thus a very desirable chemoselectivity in deoxygenation is attainable. 

Direct Deoxygenative Allylation of Substituted Benzylic Alcohols... 

A direct deoxygenation of alcohols that are capable of forming relatively stable carbanions has been reported. The alcohol reacts with potassium to form its alkoxide, which is treated with pentacarbonyliron acidic work-up furnishes the alkane (43— 90%) together with dimerized and dehydrated products in some cases. ... 

A direct deoxygenation/carbonyl addition procedure for preparing branched-chain lactones is depicted in Scheme 6. Several other examples are given in the report and the reaction is also applicable to 1,4-lactone derivatives. 

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