Carbonyl compounds reductive deoxygenation

The present preparation illustrates a general and convenient method for a two-step deoxygenation of carbonyl compounds to olefins. Related procedures comprise the basic decomposition of p-toluenesulfonylhydrazones, the hydride reduction of enol ethers, enol acetates, enamines, the reduction of enol phosphates (and/or enol phosphorodiamidates) by lithium metal in ethylamine (or liquid ammonia),the reduction of enol phosphates by titanium metal... 

Both unsymmetrical diols and alkenes can be prepared by applying these methods to mixtures of two different carbonyl compounds. An excess of one component can be used to achieve a high conversion of the more valuable reactant. A mixed reductive deoxygenation using TiCl4/Zn has been used to prepare 4-hydroxytamoxifen, the active antiestrogenic metabolite of tamoxifen. 

Deoxygenation of carbonyl compounds (6, 98 7, 54 8, 79-80). This easily prepared borane is as effective as catechol borane for reduction of tosylhydrazones of carbonyl compounds to the corresponding methylene compounds. 

The deoxygenation of epoxides is not of great preparative value since it involves some loss of stereochemical integrity and the alkenes produced are more readily approached in other ways. Reductive cleavage of ozonides, for example, using triphenylphosphine, commonly forms part of the ozonolysis procedure for conversion of alkenes into carbonyl compounds. If a carbonyl compound is treated with an appropriate P(III) reagent then the reverse process may occur—reductive coupling to form a new C=C double bond. This has found a particularly important... 

Chemical reductions of carbonyl compounds into hydroxy derivatives are more often and various reducing agents were used. Stepwise deoxygenation of diketone 166 included LAH reduction as a first step toward obtaining structure 167 (Scheme 32), which was obtained as a 2.5 1 mixture of as- and trans-isomers < 1995J(P 1)1137>. 

The Z-isomer arises from a consecutive induction of active metallic titanium surface to the polydented pinacolic intermediate formed by homolytic coupling of a radical anion species generated from reduction of two carbonyl compounds that is followed by subsequent demetallation and deoxygenation reactions. In this regard, the phenoxy-Ti-sulfone induction plays the key role for Z-stereoselection by forcing the phenoxy and sulfone moieties to be positioned on the same side. 

In situ reduction of tosylhydrazones by NaBHjCN provides an efficient method for the deoxygenation of carbonyl compounds to furnish the corresponding hydrocarbons (see also Section 3.4). In the case of tosylhydrazones derived from a,P-unsaturated carbonyl compounds, the reduction leads to a stereoselective migration of the double bond to give the corresponding tran -alkene. 

Yoneda, R., Osaki, H., Harusawa, S., and Kurihara, T., Reductive deoxygenation of a,P-unsatured ketones via cyanophosphates by lithium in liquid ammonia, Chem. Pharm. Bull., 37, 2817, 1989. Yoneda. R.. Osaki, T., Harusawa, S., and Kurihara, T., Dephosphorylation of cyano diethyl phosphates by reduction with lithium-liquid ammonia. An efficient method for conversion of carbonyl compounds into nitriles.. 1. Chem. Soc.. Perkin Trans. 1, 607, 1990. 

Well-defined arene complexes of Group 4 metals in various oxidation states have been isolated. The air- and moisture-sensitive complexes Ti(r -arene)2 (56) have a sandwich structure similar to that of the related chromium compounds [176-178]. They have been used for deoxygenation of propylene oxide and coupling reaction of organic carbonyl compounds [179]. The first synthesis of 56 was cocondensation of metal vapor with arene matrix [176]. Two more convenient methods are reduction of TiCl4 with K[BEt3H] in arene solvent [180] and reaction of TiCl4(THF)2 with arene anions followed by treatment with iodine [170,176]. The latter method involves the formation of an anionic titanate complex, [Ti(ri -arene)2] (57), which can also be formed from KH and 56 [181]. 

Deoxygenation of carbonyl compounds. Hydrous Sn02 is prepared from SnCU by precipitation with aqueous ammonia then drying and calcination at 300°C for 5 h. The reduction of aliphatic carboxylic acids gives the corresponding alcohols, whereas aromatic acids are further reduced to the hydrocarbons. Aromatic ketones also give hydrocarbons. 

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