Alcohols, allylic from alkanes

The complex 8, formed by the addition of 2-propenylmagnesium chloride to 7, adds to aromatic aldehydes, 1-alkanals, a-branched and unbranched alkanals uniformly from the 7 c-face leading to hoinoallylic alcohols with 88-94% ee35 (Method A). After hydrolytic workup, both components can be recycled. Allyl complexes 10, generated from 9, prefer 67-attack and lead to the ent-homoallylic alcohols with excellent enantioselectivity36 (Method B) (Table 8). 

Although the unsaturated nitrile oxides 124 can be prepared via the aldoxime route (see Scheme 8), the older procedure suffers from the disadvantage that a tenfold excess of allyl alcohol and two additional steps are required when compared to Scheme 15. Therefore, unsaturated nitro ether 123 that can be prepared by condensation of an aldehyde 120 and a nitro alkane followed by Michael addition of alcohol 122, was a useful precursor to nitrile oxide 124 [381. The nitrile oxide 124 spontaneously cyclized to ether 125. This procedure is particularly suitable for the synthesis of tetrahydrofurans (125a-h) and tetrahydropyrans (125i-k) possessing Ar substituents in 72-95% yield (Table 12). The seven-membered ether 1251 was obtained only in 30% yield on high dilution. The acetylenic nitro ether 126 underwent INOC reaction to provide the isoxazole 127. 

Logarithms of retention indices of alkyl benzenes specific retention volumes of esters, aldehydes and alcohols and retention times of alkanes and alkanes have been correlated with Equations 13 snd 15 or relationships derived from them (l3.). Logarithms of retention times of allyl alkyl ethers on various column packings have also been successfully correlated with Equation 15 (lA). 

Deoxygenation. Alkanes are obtained from alcohols by reaction with PdClj-EtjSiH (by adding an alkyl halide such as Mel to the reaction medium the halides are produced). Secondary allylic alcohols and acetates are reduced to the hydrocarbons with EtjSiH-LiClO. The facile removal of the oxygen atom from aryl ketones by TiCl -mediated reaction with Et,SiH makes the synthesis of a-amino acids containing carbon chains of different length and a terminal aryl group much easier. A synthesis of CHIRAPHOS via the phosphine oxides calls for deoxygenation with HSiCl -EtaN." ... 

Very few examples on the cleavage of C-O bonds in alcohols except for allylic alcohols have been reported. The highly oxophilic nature of tungsten chlorides causes abstraction of oxygen from methanol or ethanol yielding oxotungsten and bis(alkoxide)tungsten complexes with liberation of alkanes (Eq. 46) [107, 108]. 

Acetylenic carbinols, which are manufactured from aldehydes or ketones and acetylenes, can be partially hydrogenated, with the exception of propargyl alcohol itself. Hydrogenolysis is a minor side reaction unless the hydrogenation is completed to the alkane. Nickel boride (PI or P2) catalysts achieve the saturation of propargyl and allylic compounds in the presence of double bonds without hydrogenolysis, such as in 2 an intermediate in the total synthesis of the sesquiterpene sesquicarene ... 

Organolithiums. Allylic and benzylic alcohols undergo deoxygenative lithiation by treatment of their lithium alkoxides or phenyldimethylsilyl ethers with LDTBB. Alkyl phenyl selenides are also cleaved to give organolithium species that can react with aldehydes and allyl bromide. Some special alkyllithiums have been prepared from (2-pyridylthio)alkanes, which are available from carboxylic acids. ... 

Full details have appeared of the deoxygenation of alcohols to alkanes by tripropylsilane reduction of their chloroformate esters (2,122). In a related procedure, alcohol selenocarbonates (69), prepared from the chloroformate esters, have been reduced to alkanes by tributyltin hydride. Both are believed to be radical-chain reactions. Primary allylic alcohols have been deoxygenated to terminal alkenes by the new stannylation-protodestannylation sequence shown in Scheme 32 the S-Sn exchange is another radical process. The intermediate allylstannanes may alternatively undergo a new oxidative destanny-lation as shown to give overall [l,3]-transposition of the allylic alcohol. ... 

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