Subject allylic alcohols

Hydroformylation of 2,6-dimethyl-6-hepten-2-ol produces hydroxycitronellal (equation 12).22 Subjecting allyl alcohol to hydroformylation reaction conditions with HCo(CO>4 yields only propanal, isomerization taking place more rapidly than hydroformylation.2 Phosphine-modified rhodium catalysts will convert allyl alcohol to butane-1,4-diol under mild conditions in the presence of excess phosphine, however (equation 13).5 30 31 When isomerization is blocked, hydroformylation proceeds normally (equation 14). An elegant synthesis of the Prelog-Djerassi lactone has been accomplished starting with the hydroformylation of an allylic alcohol (equation IS).32... 

The idea enabled a domino process by combining copper-catalyzed C-O bond formation and thermal Claisen rearrangement. Subjecting allylic alcohol and vinyl iodide to the reaction conditions led to the clean formation of the desired rearrangement product in 55% yield with high stereochemical purity (Eq. 3.1.15). The preparation of two adjacent quartemary stereocenters from geraniols is successfully prepared using the aforementioned reaction conditions (Eq. 3.1.16). 

When the furanones 110 (R = Ph, p-MeOC6H4, p-Cl—C6H4) were subjected to reduction using sodium borohydride, neither the glycols 111 nor the allyl alcohols 112 were formed. Instead, the corresponding 4-(arylmethylene)-2,3-(4//,5// )-furandiones 113 were obtained (Scheme 34) (86JHC199). 

The construction of key intermediate 18 can be conducted along similar lines. Sharpless asymmetric epoxidation of allylic alcohol 22 using (+)-DET furnishes epoxy alcohol 52b (Scheme 11). Subjection of the latter substance to the same six-step reaction sequence as that leading to 54a provides allylic alcohol 54b and sets the stage for a second SAE reaction. With (+)-DET as the... 

Owing to the reversible nature of the allylic sulfenate/allylic sulfoxide interconversion, the stereochemical outcome of both processes is treated below in an integrated manner. However, before beginning the discussion of this subject it is important to point out that although the allylic sulfoxide-sulfenate rearrangement is reversible, and although the sulfenate ester is usually in low equilibrium concentration with the isomeric sulfoxide, desulfurization of the sulfenate by thiophilic interception using various nucleophiles, such as thiophenoxide or secondary amines, removes it from equilibrium, and provides a useful route to allylic alcohols (equation 11). 

Trifluoromethanesulfonates of alkyl and allylic alcohols can be prepared by reaction with trifluoromethanesulfonic anhydride in halogenated solvents in the presence of pyridine.3 Since the preparation of sulfonate esters does not disturb the C—O bond, problems of rearrangement or racemization do not arise in the ester formation step. However, sensitive sulfonate esters, such as allylic systems, may be subject to reversible ionization reactions, so appropriate precautions must be taken to ensure structural and stereochemical integrity. Tertiary alkyl sulfonates are neither as easily prepared nor as stable as those from primary and secondary alcohols. Under the standard preparative conditions, tertiary alcohols are likely to be converted to the corresponding alkene. 

Apart from modifications in the bulk, also surface modification of PHAs has been reported. Poly(3HB-co-3HV) film surfaces have been subjected to plasma treatments, using various (mixtures of) gases, water or allyl alcohol [112-114]. Compared to the non-treated polymer samples, the wettability of the surface modified poly(3HB-co-3HV) was increased significantly [112-114]. This yielded a material with improved biocompatibility, which is imperative in the development of biomedical devices. 

A method for microwave-assisted transesterifications has been described by Van-den Eynde and Rutot [73], The authors investigated the microwave-mediated deriva-tization of poly(styrene-co-allyl alcohol) as a key step in the polymer-assisted synthesis of heterocycles. Several /i-ketoesters were employed in this procedure and multigram quantities of products were obtained when neat mixtures of the reagents in open vessels were subjected to microwave irradiation utilizing a domestic micro-wave oven (Scheme 7.65). The successful derivatization of the polymer was confirmed by IR, 1H NMR, and 13C NMR spectroscopic analyses. The soluble supports... 

Kissel, Ramsden, and other researchers at Pfizer and Chirotech jointly published a novel chiral synthesis of pregabalin (2) in 2003 based on asymmetric hydrogenation (Burk et al., 2001, 2003). Their synthesis started with the condensation of isobutyralde-hyde with acrylonitrile under Baylis-Hillman conditions to give allylic alcohol 65. This alcohol was activated as the carbonate 66 and subjected to palladium-catalyzed car-bonylation conditions to give cyanoester 67. The ester 67 was hydrolyzed and converted to... 

In the epoxidation of acyclic allylic alcohols (Scheme 6), the diastereoselectivity depends significantly on the substitution pattern of the substrate. The control of the threo selectivity is subject to the hydroxyl-group directivity, in which conformational preference on account of the steric interactions and the hydrogen bonding between the dioxirane oxygen atoms and the hydroxy functionality of the allylic substrate steer the favored 7r-facial... 

In the second approach, allylboronation of 9 with 10 led to the predominant formation of 8a which was transformed to 6a (R = H). The allylic alcohols 5a and 5b prepared from 6a and 6b, respectively, were subjected to asymmetric epoxidations307, each with (-f)-DET and (—)-DET, to provide four diastereomers. One of them, 4b, was identical with degradation product 2. Note that in these reactions double stereodifferenlialion (see Section A.2.3.5.4.) is operating (for configurational assignment at C-15, see p431)244. 

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