Conversion to allylic alcohols

Catalyst Temp., Conversion to allyl alcohol, % of acrolein °C fed Allyl alcohol yield, % of acrolein consumed... 

Conversion of a-haloketones to olefins using hydrazine (via enedlitnides C-C-N NH). Also reduction of o,3-epoxy ketones to allyl alcohols. 

The model procedure described above is applicable to allylic alcohols, ethers, and acetates. The submitters results for the conversion of several such compounds to the corresponding olefins, performed on a smaller... 

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. 

For a review of the conversion of allylic alcohols to allylic halides, see Magid, R.M. 

One of the most active and selective catalysts in this kind of reaction is undoubtedly Ir/support, as recently demonstrated by Jacobs and coworkers [276], Therefore, by combining the carbonyl affinity of metallic iridium with the promotion effect of the H-fl zeolite, which is a strong Bronsted acid, one can reduce a large variety of unsaturated ketones and aldehydes to allylic alcohols with high conversions, selectivities, and diasteieoselectivities. 

The present method offers a more efficient and convenient two-step route to the parent a,B-unsaturated acylsilane derivative. The first step in the procedure involves the conversion of allyl alcohol to allyl trimethylsilyl ether, followed by metalation (in the same flask) with tert-butyllithiura at -75°C. Protonation of the resulting mixture of interconverting lithium derivatives (2 and 3) with aqueous ammonium chloride solution furnishes (1-hydroxy-2-propenyl)trimethylsilane (4), which is smoothly transformed to (1-oxo-2-propenyl)trimethylsilane by Swern oxidation. The acylsilane is obtained in 53-68% overall yield from allyl alcohol in this fashion. 

TABLE 8.18. CONVERSION OF ALLYLIC ALCOHOLS TO P-AMINO ALCOHOLS VIA OXAZOLINES... 

OXAZOLINES FROM NITRILES AND AMINO ALCOHOLS, 385-386 OXAZOLINES FROM IMIDATES AND AMINO ALCOHOLS, 388-389 CONVERSION OF ALLYLIC ALCOHOLS TO P-AMINO ALCOHOLS VIA OXAZO-... 

Lygo, B. and To, D.C.M., Asymmetric Epoxidation via Phase-transfer Catalysis Direct Conversion of Allylic Alcohols into a, -Epoxyketones. Chem. Commun. 2002, 2360-2361. 

Because of the mildness of the procedure, this is probably the best means of accomplishing this conversion. The selenoxide reaction has been used in a procedure for the conversion of epoxides to allylic alcohols.229... 

Deoxygenation of allyttc alcohols.3 A method for conversion of allylic alcohols to l-alkenes is outlined in equation (I). The first step is an allylic rearrangement of an Oallyl xanthate to 2. The second step is an allyl transfer from sulfur to tin with tri-n-butyltin hydride to give the allylic stannane (3). The last step, destannylation, is a well-known mule to terminal alkcnes.4... 

AUyttc chlorides (8, 516). The use of these two reagents for conversion of allylic alcohols to the largely unrearranged allylic chloride has been improved by use of... 

To determine the purity of any sample of allyl alcohol, 1 cc. is run into 15 to 25 cc. of carbon tetrachloride and this solution is then treated in the cold with a carbon tetrachloride solution of bromine (standardized with potassium iodide and sodium thiosulfate) until a permanent bromine coloration is obtained. The amount of allyl alcohol present in any solution may also be determined roughly by conversion to allyl bromide. From several experiments it was found that the allyl bromide obtained was equivalent to the amount of allyl alcohol as determined by bromine titration. 

Conjugate carbonyl compounds contain centers of different hardness (hard Co and soft C=C), consequently hard hydrides favour conversion of enones to allylic alcohols [25]. Such a concept could be operative also in our case since C=C bond is preferably reduced on going from Mgo to SrO. 

Several factors contribute to the frequent use of (3 )-substituted allylic alcohols (13) for asymmetric epoxidation (a) The allylic alcohols are easily prepared (b) conversion to epoxy alcohol normally proceeds with good chemical yield and with better than 95% ee (c) a large variety of functionality in the (3E) position is tolerated by the epoxidation catalyst. Representative epoxy alcohols (14) are summarized in Table 6A.4 [2,4,18,41-53] and Figure 6A.3 (4,54-61], with results divided arbitrarily according to whether the (3E) substituent is a hydrocarbon (Table 6A.4) or otherwise (Fig. 6A.3). The versatility of these and other 3-substi-tuted epoxy alcohols for organic synthesis is illustrated with several examples in the following discussion. 

The ratio of the rates of epoxidation of the two enantiomers, las/ s]ow, has been defined as the relative rate ( rel) and is related to the percent conversion of allylic alcohol to epoxy alcohol and the enantiomeric purity of the remaining allylic alcohol. A mathematical relationship between these variables exists and can be represented graphically as shown in Figure 6A.5 [14]. 

Kinetic resolution of chiral aUylic alcohols.7 Partial (at least 60% conversion) asymmetric epoxidation can be used for kinetic resolution of chiral allylic alcohols, particularly of secondary allylic alcohols in which chirality resides at the carbinol carbon such as 1, drawn in accordance with the usual enantioface selection rule (Scheme I). (S)-l undergoes asymmetric epoxidation with L-diisopropyl tartrate (DIPT) 104 times faster than (R)-l. The optical purity of the recovered allylic alcohol after kinetic resolution carried to 60% conversion is often > 90%. In theory, any degree of enantiomeric purity is attainable by use of higher conversions. Secondary allylic alcohols generally conform to the reactivity pattern of 1 the (Z)-allylic alcohols are less satisfactory substrates, particularly those substituted at the /1-vinyl position by a bulky substituent. 

Scheme 3.13 Direct conversion of allylic alcohols to epoxyketones.

The same concept is applicable to allylic alcohols, ketones, or ketoximes. Enol acetates or ketones were successfully converted in multi-step reactions to chiral acetates in high yields and optical yields through catalysis by Candida antarctica lipase B (CALB, Novozyme 435) and a ruthenium complex. 2,6-Dimethylheptan-4-ol served as a hydrogen donor and 4-chlorophenyl acetate as an acyl donor for the conversion of the ketones (Jung, 2000a). 

In this process, the fine powder of lithium phosphate used as catalyst is dispersed, and propylene oxide is fed at 300°C to the reactor, and the product, allyl alcohol, together with unreacted propylene oxide is removed by distillation. By-products such as acetone and propionaldehyde, which are isomers of propylene oxide, are formed, but the conversion of propylene oxide is 40 percent and the selectivity to allyl alcohol reaches more than 90 percent. Allyl alcohol obtained by this process may contain small amounts (<1%) of propanol. 

The synthesis of (+)-pisiferic acid (1) presents many important aspects (i) functionalization of the angular methyl group to lactone, (ii) cleavage of lactone ring to carboxylic acid, and (iii) conversion of (78) to allylic alcohol (81) via iron carbonyl complex... 

Fig (10) The iron complex (80), prepared from methyl abietate (79) is converted to compound (81) utilizing standard organic reactions. It was converted to allylic alcohol (82) by treatment with iodine and potassium bicarbonate. The ketone (83) obtained from (82) undergoes aromatization on bromination and dehydrobromination. Yielding (84) whose transformation to lactone (87) is accomplished following the similar procedure adopted for the conversion of (68) to (74). It is converted to pisiferic acid (1) by treatment with aluminium bromide in... 

Fig (22) 2-isopropylphenol (183) is converted to allylic alcohol (185). Its bromide derivative reacts with methyl acetoacetate. The resulting compound undergoes radical cyclization yields ketoester (186) whose vinyl triflate on reduction and carbonylation furnishes lactone (187). Diol (188) obtained from (187), is converted to monoepoxide (189) which on further epoxidation produces triptonide (148). Its conversion to triptolide (149) is accomplished by reduction. 

---