Allylic alcohol transformation

Allylic Alcohols. Full details have appeared of the conversion of epoxides into allylic alcohols, mediated by trimethylsilyl trifluoromethanesulphonate (Scheme 4) (see 6,163 4,145), and this sequence is mentioned in a review of trialkylsilyl perfluoroalkanesulphonates as reagents opening of an epoxide ring occurs at the more substituted centre. The use of trimethylsilyl iodide for the epoxide-allyl alcohol transformation (5, 158) is discussed in a review of the preparation and applications of this reagent. ... 

A catalytic enantio- and diastereoselective dihydroxylation procedure without the assistance of a directing functional group (like the allylic alcohol group in the Sharpless epox-idation) has also been developed by K.B. Sharpless (E.N. Jacobsen, 1988 H.-L. Kwong, 1990 B.M. Kim, 1990 H. Waldmann, 1992). It uses osmium tetroxide as a catalytic oxidant (as little as 20 ppm to date) and two readily available cinchona alkaloid diastereomeis, namely the 4-chlorobenzoate esters or bulky aryl ethers of dihydroquinine and dihydroquinidine (cf. p. 290% as stereosteering reagents (structures of the Os complexes see R.M. Pearlstein, 1990). The transformation lacks the high asymmetric inductions of the Sharpless epoxidation, but it is broadly applicable and insensitive to air and water. Further improvements are to be expected. 

The essential features of the Masamune-Sharpless hexose synthesis strategy are outlined in a general way in Scheme 4. The strategy is based on the reiterative- application of a two-carbon extension cycle. One cycle comprises the following four key transformations (I) homologation of an aldehyde to an allylic alcohol (II) Sharpless asymmetric epoxidation of the allylic alcohol ... 

Schemes 28 and 29 illustrate Curran s synthesis of ( )-hirsutene [( )-1]. Luche reduction58 of 2-methylcyclopentenone (137), followed by acetylation of the resulting allylic alcohol, furnishes allylic acetate 138. Although only one allylic acetate stereoisomer is illustrated in Scheme 28, compound 138 is, of course, produced in racemic form. By way of the powerful Ireland ester enolate Clai-sen rearrangement,59 compound 138 can be transformed to y,S-unsaturated tm-butyldimethylsilyl ester 140 via the silyl ketene acetal intermediate 139. In 140, the silyl ester function and the methyl-substituted ring double bond occupy neighboring regions of space, a circumstance that favors a phenylselenolactonization reac-...

Aziridine lactone 235 (Scheme 3.87) underwent ring-opening with allyl alcohol to give a 53% yield of a-amino lactone 236, which was successfully transformed to the unnatural enantiomer of polyoxamic acid (—)-237 [32],... 

The Sharpless-Katsuki asymmetric epoxidation (AE) procedure for the enantiose-lective formation of epoxides from allylic alcohols is a milestone in asymmetric catalysis [9]. This classical asymmetric transformation uses TBHP as the terminal oxidant, and the reaction has been widely used in various synthetic applications. There are several excellent reviews covering the scope and utility of the AE reaction... 

The procedure is outlined in Scheme 8.33, starting from the generic allylic alcohol 125. SAE on 125 would provide epoxide 126, which could easily be transformed into the unsaturated epoxy ester 127 by oxidation/Horner-Emmonds olefmation (two-carbon extension). This operation makes the oxirane carbon adjacent to the double bond more susceptible to nucleophilic attack by a hydride, so reductive opening (DIBAL) of 127 provides, with concomitant ester reduction, diol 128. Pro-... 

The spontaneous rearrangement of allyl p-toluenesulphenates to allyl sulphoxides was independently recorded by Mislow and coworkers and Braverman and Stabinsky. Mislow and colleagues201 have demonstrated that simple allyl alcohols such as 149, on conversion to the corresponding lithium alkoxides followed by treatment with arenesulphenyl chlorides, may be smoothly transformed at room temperature via the sulphenate esters into allylic sulphoxides 150 (equation 83). Braverman and Stabinsky202 have found that when the more reactive trichloromethanesulphenyl chloride is treated with allyl alcohol and pyridine in ether at — 70°, it affords trichloromethyl allyl sulphoxide and not allyl trichloromethanesulphenate as reported by Sosnovski203 (equation 84). 

The data presented demonstrate that allylic sulfoxides can provide an easy and highly stereoselective route to allylic alcohols taking advantage of the facility of the allylic sulfoxide-sulfenate [2,3]-sigmatropic rearrangement. This is of considerable synthetic utility, since a number of stereoselective and useful transformations of allylic alcohols and their derivatives have become available in recent years107-109. 

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. 

Overman LE, Owen CE, Pavan MM, Richards CJ (2003) Catalytic asymmetric rearrangement of allylic N-aryl trifluoroacetimidates. A useful method for transforming prochiral allylic alcohols to chiral allylic amines. Org Lett 5 1809-1812... 

DKR reactions were performed with lipase and Pd(PPh3)4 in the presence of dppf and 2-propanol in THF. 2-Propanol was used as an acyl acceptor. Various acyclic allyhc acetates were transformed to their corresponding allylic alcohols at room temperature in good yields and excellent optical purities (Table 16). 

The surface transformations of propylene, allyl alcohol and acrylic acid in the presence or absence of NHs over V-antimonate catalysts were studied by IR spectroscopy. The results show the existence of various possible pathways of surface transformation in the mechanism of propane ammoxidation, depending on the reaction condition and the surface coverage with chemisorbed NH3. A surface reaction network is proposed and used to explain the catalytic behavior observed in flow reactor conditions. 

The adsorption of allyl alcohol thus readily gives rise to an allyl alcoholate species at room temperature. At higher temperatures this species first transforms to chemisorbed acrolein and then to an acrylate species. 

Co-adsorption experiments show a complex role of the nature and concentration of chemisorbed ammonia species. Ammonia is not only one of the reactants for the synthesis of acrylonitrile, but also reaction with Br()>nsted sites inhibits their reactivity. In particular, IR experiments show that two pathways of reaction are possible from chemisorbed propylene (i) to acetone via isopropoxylate intermediate or (ii) to acrolein via allyl alcoholate intermediate. The first reaction occurs preferentially at lower temperatures and in the presence of hydroxyl groups. When their reactivity is blocked by the faster reaction with ammonia, the second pathway of reaction becomes preferential. The first pathway of reaction is responsible for a degradative pathway, because acetone further transform to an acetate species with carbon chain breakage. Ammonia as NH4 reacts faster with acrylate species (formed by transformation of the acrolein intermediate) to give an acrylamide intermediate. At higher temperatures the amide may be transformed to acrylonitrile, but when Brreform ammonia and free, weakly bonded, acrylic acid. The latter easily decarboxylate forming carbon oxides. 

The enantioselective epoxidation method developed by Sharpless and co-workers is an important asymmetric transformation known today. This method involves the epoxidation of allylic alcohols with fcrt-butyl hydroperoxide and titanium (sopropoxide in the presence of optically active pure tartarate esters, see Eqn. (25). 

The allylic hydroperoxides generated by singlet oxygen oxidation are normally reduced to the corresponding allylic alcohol. The net synthetic transformation is then formation of an allylic alcohol with transposition of the double bond. 

Synthesis of Allylic Alcohol Xa. A 3.84 g sample of olefin VII was treated with m-chloroperoxybenzoic acid (MCPBA) in dichloromethane for 1.5 hours at 0°C and 2.5 hours at 20°C. The NMR spectrum of the crude product indicated a mixture of approximately 75% epoxide VIII and 25% IX (structural assignments based upon assumed epoxidation preferentially from the less hindered side). Purification by column chromatography furnished 0.61 g of IX and 2.58 g of VIII. The separation was performed for characterization purposes the crude epoxidation mixture was suitable for subsequent transformations. 

The presence of V does not diminish the activity of a grafted Ti-Si02 catalyst for olefin epoxidation. However, activity towards simple olefins such as cyclohexene is not enhanced. Since homogeneous V catalysts are known to catalyze the epoxidation of functionalized olefins (e.g., allylic alcohols), the ability of a mixed V-Ti/Si02 catalyst to achieve such transformations will be the next focus of our investigations. 

Knowledge regarding biosyntheses has induced several biomimetic approaches towards steroids, the first examples being described by van Tamelen [10] and Corey [11]. A more efficient process was developed by Johnson [12] who, to synthesize progesterone 0-10 used an acid-catalyzed polycyclization of the tertiary allylic alcohol 0-7 in the presence of ethylene carbonate, which led to 0-9 via 0-8 (Scheme 0.3). The cyclopentene moiety in 0-9 is then transformed into the cyclohexanone moiety in progesterone (0-10). 

Another domino process, designed by Polt and coworkers [16], deals with the consecutive transformation of an in situ-prepared aldehyde to give 3-amino allylic alcohols 7-31 from 3-amino acids. When the 3-amino acid ester derivative 7-29 is sequentially treated with iBu5Al2H and vinyl magnesium bromide, a 3 2 mixture of the allylic alcohol derivatives 7-30 is obtained in 60% yield, which can be hydrolyzed to give 7-31 (Scheme 7.10). 

There are many ways to categorize the oxidation of double bonds as they undergo a myriad of oxidative transformations leading to many product types including epoxides, ketones, diols, endoperoxides, ozonides, allylic alcohols and many others. Rather than review the oxidation of dienes by substrate type or product obtained, we have chosen to classify the oxidation reactions of dienes and polyenes by the oxidation reagent or system used, since each have a common reactivity profile. Thus, similar reactions with each specific oxidant can be carried out on a variety of substrates and can be easily compared. 

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