Allylic diols

The masked propargylic anfz-l,3-diols obtained in these reactions are useful precursors to more functionalized systems. Lindlar reduction of alkyne 171 generated the (Z)-allylic diol 172, which underwent diastereoselective osmium tetraoxide-catalyzed dihydroxylation to provide the partially protected tetraol 173 (Scheme 28). The propargylic anfz-l,3-dioxane 175,obtained in 88% yield from... 

The catalytic enantioselective desymmetrization of meso compounds is a powerful tool for the construction of enantiomerically enriched functionalized products." Meso cyclic allylic diol derivatives are challenging substrates for the asymmetric allylic substitution reaction owing to the potential competition of several reaction pathways. In particular, S 2 and 5n2 substitutions can occur, and both with either retention or inversion of the stereochemistry. In the... 

This procedure illustrates a fundamentally new method for constructing substituted tetrahydrofurans.5-10 This practical method assembles the tetrahydrofuran ring from allylic diol and carbonyl components and in the process forms three ring bonds C(2)-C(3), C(4)-C(5) and 0-C(5). Both aldehydes (eq 1) and ketones (illustrated in the present procedure) can be employed as the carbonyl component. Although it is often convenient to isolate the acetal intermediate, conversion to the 3-acyltstrahydrofuran can also be accomplished in many cases by the direct reaction of the diol and carbonyl components.8 High ds stereoselectivity (at least 20 1) is observed in the preparation of tetrahydrofurans that contain single side chains at carbons 2 and 5 (eq 1). The kinetically controlled product also has the cis relationship of these side chains and the 3-acyl substituent. 

A definitive feature of this highly stereoselective new route to substituted tetrahydrofurans is that both syn and anti allylic diol stereoisomers typically afford identical tetrahydrofuran products. Thus, there is no need for stereoselective... 

Overman reported the synthesis of highly enantiopure 3-acyltetrahydrofurans with C5 substituents from formaldehyde acetals of allylic diols <00TL9431>. An example of Overman s procedure is depicted below, which involves the generation of a formaldehyde oxonium ion intermediate 92 before the cyclization. 

This rearrangement of allylic acetals can also be used for furan annelations, in which the formation of the new tetrahydrofuran ring is coupled with ring enlargement of the starting ring.3 The same dr-fused bicyclic tetrahydrofuran is formed from either one of the cis- or mwr-allylic diols used as starting materials. 

Reductive elimination of an allylic diol group. A new synthesis of vitamin A involves reduction of the allylic diol 1, prepared in several steps from JJ-ionone, with a low valent titanium formed from TiCl3 and LiAlH, in the ratio 2 1. Thus, the allylic diol group of 1 [either (E) or (Z)] is reduced to an (E,E)-1,3-diene group to form the silyl ether (2) of vitamin A.1 When the primary hydroxyl group is protected as an acetate, the reduction gives a mixture of (E)- and (Z)-2. 

The same catalytic system (SeOi/TBHP) has also been used by Chabaud and Sharpless in the allylic oxidation of alkynes. The oxidation products resulting from the Se02-catalyzed allylic oxidation with TBHP are the allylic alcohol, the allylic diol, the allylic ketone, the ketol and the enynone (Scheme 127). The main product of the reaction is either the alcohol or the diol, depending on the substrate employed (together 76-100% of the whole yield). The yields of allylic oxidation products together range from 15 to 88%. From the observed results with unsymmetrical alkynes it could be concluded that the reactivity sequence for the carbon attached to the triple bond of alkynes is CH2 CH > CH3. 

This work and parallel studies by another group5 have been used to assign the threo-configuration to the allylic diol group in the side chain of the frog poison pumiliotoxin B (5). 

Trienols. Solladie has extended his reductive elimination of allylic diols with TiCl3-LiAlH4 (2 1) to a synthesis of optically active trienols from chiral allylic diols. 

Syn- and ft -l,5-allylic diols 224 undergo stereospecific intramolecular palladium-catalyzed cyclizations to afford syn- or //-2,6-disubstituted 3,6-dihydropyrans the stereochemistry of the 3,6-dihydropyran product is defined by that of the starting diol (Scheme 64) <2005TA1299>. 

Allyl amines can also be formed by desymmetrization of allyl diols with tosyl isocyanate in the presence of chiral palladium complexes [19d,27]. Trost et al., as well as others, have recently used this approach for the synthesis of natural products [28]. 

When 125 was subjected to a two-step sequence, reductive cleavage of the 0-0 bond and subsequent oxidative dehydration, by treatment with zinc in AcOH, the allylic diol 135 and the 1,2-oxazocine 126, as minor product, were isolated. Oxidation of the diol 135 under several different reaction conditions (pyridinium chlorochromate (PCC), 2-iodoxybenzoic acid (IBX)/EtOH, IBX/DMSO, Pyr/SOj) gave 126 in high yield (68-92%), while with tetrapropylammonium perruthenate/Wmethylmorphaline Ar-oxidc (TPAP/NMO) as oxidizing agent 126 was the minor product and the a,/3-unsaturated 7-butyrolactone 136 was obtained in 68% yield (Scheme 28) <2005JOC6995>. 

The first step is Pd catalyzed aUylation, and the second step is (3a) catalyzed cross metathesis of a protected allylic diol with yields over the two-step process in the 40 60% range (equation 18). 

Brown, M. J., Harrison, T., Herrinton, P. M., Hopkins, M. H., Hutchinson, K. D., Overman, L. E., Mishra, P. Acid-promoted reaction of cyclic allylic diols with carbonyl compounds. Stereoselective ring-enlarging tetrahydrofuran annulations. J. Am. Chem. Soc. 1991,113, 5365-5378. 

The relatively efficient cyclisation of monocyclofamesic acid with boron trifluoride etherate to methyl bicyclofarnesate (46) has led to a successful synthesis of drimenin (48) via acid-catalysed lactonisation of the allylic alcohol (47), a product of singlet oxygen addition to (46). It has also been shown that hydride reduction of drimenin to the allylic diol (49) followed by a two-step oxidation procedure yields cinnamolide (39). A Ci antifungal mould metabolite has... 

Thus, the bifunctional allylic diol 12 was reacted with 2-methoxy-3-mcthyl-l,3-butadiene in refluxing xylene in the presence of an acid and reduced with sodium borohydride to give 2,6.11,15-tetramcthyl-l,6,10,15-hexadecatetraene-3.14-diol (13), which can be transformed to the symmetrical triterpene squalene28-224. 

In an effort to establish the configuration of the allylic diol functionality of pumiliotoxin B, Overman [105] synthesized syn and anti- o s 305 and 306 using lactic acid to set the... 

A second new synthesis of squalene utilizes the observation that selenium dioxide oxidation of gem-dimethyl olefins or cis- and truns-allylic alcohols yields stereospecifically traus-aj3-unsaturated aldehydes. The olefin (4) or a mixture of cis- and truus-diols (5) were transformed by use of selenium dioxide, followed by reduction, into the truns-allylic diol (6). The corresponding bromide (7) was used to alkylate two moles of the ylide from trans-geranyltributylphosphonium bromide leading eventually to all-traus-squalene in 46% yield [from the diol (6)]. Protection of one of the p-alcohol groups of (6) as the tetrahydropyranyl ether opens the possibilities of unsymmetrical coupling and the introduction of specifically labelled fragments. 

Biannic, B. Gold-Catalyzed Cyclization of Mono-Allylic Diols and Ethers. Ph.D. Thesis, University of Florida Gainesville, FL, 2011. 

In some cases where there is a neighboring group participation, aldehydes are formed from terminal olefins. The aldehyde 27 was obtained cleanly by participation of the cyclic carbonate of allylic diol 26, but the normal oxidation to afford the methyl ketone 29 occurred with the unprotected diol 28 [24]. 

Heck arylation of allylic diols, with iodobenzene in the presence of potassium carbonate, resulted in phenyl-substituted diols. A selective /8-hydride elimination in a chelated ring intermediate may be responsible for this outcome (the authors suggest de-protonated cr-intermediates) (Scheme 30). Arylation of an aUylic substrate lacking the ho-moallylic hydroxy group under otherwise identical conditions furnished a mixture of products, suggesting that the aforementioned hydroxy group has an impact on the hydride elimination. 

MBH adducts have been transformed into acyloxiranes 453 by using iodo-sobenzene activated by a catalytic amount of KBr in water at room temperature. lodosobenzene has been utilized here for two-fold oxidation of a secondary alcohol of a MBH adduct followed by subsequent epoxidation of the generated enone in a one-pot synthesis of an acyloxirane (Scheme 3.199). Complementarily to the syn diasteroselectivity obtained in the direct epoxidation of MBH adducts, mono-TBS protected allylic diols 454 derived from... 

Even allylic alcohols participate in gold-catalyzed cyclizations of this type. Aponick and co-workers obtained substituted tetrahydrofui s and tetrapyrans by dehydrative cyclization of allylic diols in the presence of PhsPAuCl and AgOTf (Scheme 4-115). High cis-diastereoselectivities were observed when the reaction was carried out at low temperature (-10...-78 C). Bandini and co-workers ... 

Figure 7.7 Regioselective -hydrogen elimination in allylic diol system.

Kang, S.-K., Jung, K.-Y., Park, C.-H. et at. (1995) Palladium-catalyzed arylation of allylic diols highly selective s5mthesis of phenyl-substituted allylic diols. Tetrahedron Lett., 35, 6287-90. 

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