Alcohols, allylic => conjugated

Homoallylic alcohols. Allylation of carbonyl compounds is straightforward. Under catalyzed conditions enones undergo conjugate addition. 

It should be pointed out that manganese dioxide is a mild oxidant that usually converts primary allylic alcohols into conjugated aldehydes without significant further oxidation to carboxylic acids." However, in the presence of HCN and cyanide, the a, -unsaturated aldehydes could be converted into cyanohydrins, which are susceptible to the oxidation of Mn02 to acyl cyanides. In the presence of an alcohol, the a,j8-unsaturated esters are obtained. It should be emphasized that this reaction works only for a,j8-unsaturated aldehydes and will not cause any cis-trans isomerization for the a,/3-unsaturated double bond. For example, benzaldehyde (> 95%), cinnamaldehyde (> 95%), furfural (> 95%), geranial (85-95%), and farnesal (> 95%) have all been transformed into the corresponding methyl esters. ... 

Disubstituted vinyl silanes are epoxidized in high ee s and enantiomerically enriched 1,1-disubstituted epoxides can be obtained via the desilylation of these epoxides e.g., 18). Allylic alcohols and conjugated dienes and enynes are effective substrates (e.g. 19 and 20). ° The epoxidations of enol ethers and enol esters were also studied. The resulting epoxides (e.g., 21) from enol esters can undergo stereoselective rearrangement to give optically active a-acyloxy ketones, (5)-22 or (i )-23, under different acidic conditions. 

Scheme 9 Transfer hydrogenative couplings of 2-butyne to form allylic alcohols and conjugated enones. Yields are of material isolated by flash chromatography on silica gel...

SCHEME 23 Synthesis of Z-allylic alcohols from conjugated dienes [4]. 

Compounds containing an allyl group are susceptible to either olefinic or allylic oxidation (Figs 4.10, 4.11). Olefinic oxidation is mediated with an epoxidation step like the metabolism of secobarbital to secodiol. Allylic oxidation does not produce epoxide intermediates. The generated alcohol is conjugated with glucuronic add in phase II metabolism in order to increase the compound hydrophUi-dty and consequently the urinary excretion. An example of... 

Conjugate addition of vinyllithium or a vinyl Grignard reagent to enones and subsequent oxidation afford the 1.4-diketone 16[25]. 4-Oxopentanals are synthesized from allylic alcohols by [3,3]sigmatropic rearrangement of their vinyl ethers and subsequent oxidation of the terminal double bond. Dihydrojasmone (18) was synthesized from allyl 2-octenyl ether (17) based on Claisen rearrangement and oxidation[25] (page 26). 

The data discussed above can be summarized as follows NaBH4 is more prone to saturate conjugated double bonds than LiAlH4 the double bond in a l-en-3-one steroid is especially sensitive use of pyridine as a solvent favors formation of the saturated alcohol use of methanol with NaBH4, Na(OCH3)3BH in tetrahydrofuran, Li[OC(CH3)3]3AIH and aluminum hydride favor formation of the allylic alcohol. 

Carbonyl reduction begins to compete with olefin saturation when the double bond is hindered or the carbonyl is aromatic or an aromatic vinylog. In conjugated systems, deoxygenation may occur via an intermediate allylic alcohol (51). 

Optically active allylic alcohols can only be prepared from optically active sulfinyl epoxides when the created double bond is conjugated to an aromatic system. One example is described below29. 

In addition to the synthetic applications related to the stereoselective or stereospecific syntheses of various systems, especially natural products, described in the previous subsection, a number of general synthetic uses of the reversible [2,3]-sigmatropic rearrangement of allylic sulfoxides are presented below. Several investigators110-113 have employed the allylic sulfenate-to-sulfoxide equilibrium in combination with the syn elimination of the latter as a method for the synthesis of conjugated dienes. For example, Reich and coworkers110,111 have reported a detailed study on the conversion of allylic alcohols to 1,3-dienes by sequential sulfenate sulfoxide rearrangement and syn elimination of the sulfoxide. This method of mild and efficient 1,4-dehydration of allylic alcohols has also been shown to proceed with overall cis stereochemistry in cyclic systems, as illustrated by equation 25. The reaction of trans-46 proceeds almost instantaneously at room temperature, while that of the cis-alcohol is much slower. This method has been subsequently applied for the synthesis of several natural products, such as the stereoselective transformation of the allylic alcohol 48 into the sex pheromone of the Red Bollworm Moth (49)112 and the conversion of isocodeine (50) into 6-demethoxythebaine (51)113. 

The conjugate addition of tributylstannylmethyllithium to unsaturated sulfones 100, followed by trapping with an aldehyde, provides a route to the allyl alcohol 101 which may be transformed into 2(5H)-furanones (equation 81)67. 

Potential precursors to stereoselective INOC and ISOC reactions (e.g., 195 and 196, respectively) have been prepared via stereoselective conjugate additions of several allylic alcohols (e.g., 194,X = 0) and an allylic thiol (e.g., 194,X = S) to a chiral (E)-nitro alkene (e. g., 193) that was derived from (P)-2,3-isopropylidene... 

The classification is unaffected by allylic, vinylic, or acetylenic unsaturation appearing in both starting material and product, or by increases or decreases in the length of carbon chains for example, the reactions f-BuOH f-BuCOOH, PhCHgOH - PhCOOH, and PhCH=CHCH20H -PhCH=CHCOOH would all be considered as preparations of carboxylic acids from alcohols. Conjugate reduction and alkylation of unsaturated... 

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