Diols allylic vicinal

The carbonate of an allylic vicinal diol also suffered a very high anti-Sj l selective addition of Grignard reagent in the presence of a catalytic amount of Cul and, preferably, 1 eq of BF3 OEt2 [Eq. (58) 122]. 

With the preparation of racemic drhydroisocodeine (79), Chida reported a formal synthesis of morphine [52], The synthesis is based on a cascade of sequential Claisen rearrangements of an allylic vicinal diol derivative as key steps. The Claisen rearrangement protocol, as an efficient strategy for the installation of the C13 quaternary carbon, was successfully employed in the preparation of the Amaryllidaceae alkaloid galanthamine, published 1 year before the synthesis of dihydroisocodeinone [64],... 

The combined carbocupration of ynol ether followed by a zinc homologation in the presence of aldehydes has provided, in a single-pot operation, stereodefined allylic vicinal diol substmctures in good isolated yields and stereoselectivities (up to 92 8 dr) The stereochemistry of the final adducts suggests that the reaction 0 proceeds through a chairlike transition state in which the substituent of the aldehyde preferentially occupies a pseudoaxial position to avoid gauche interactions with an -configurated alkoxy-substituted aUylmetal species. A similar stereochemical outcome has been reported for the allylation reaction of 3,3-disubstituted allylzinc species with aldehydes. ... 

Although lead tetraacetate can attack many polar and nonpolar functions in the steroid molecule, its greatest reactivity is towards vicinal diols. These diols are generally cleaved so rapidly under stoichiometric conditions that other alcohol functions in the molecule need not be protected. Thus lead tetraacetate in acetic acid at room temperature splits the 17a,20-diol group in (9) to yield the 17-ketone (10), the allylic A -3jS-alcohol remaining intact during this oxidation. Since lead tetraacetate is solublein many anhydrous... 

Epoxides are easily attacked by trifluoroacetic anhydride. The reactions lead to diesters of vicinal diols and monoesters of unsaturated allylic alcohols in ratios depending on the reaction conditions [24] (equation 13). 

With sodium borohydride and catalytic amounts of titanyl acetoacetonate, a,fi-unsaturated carbonyl compounds give allyl alcohols regioselectively, whereas a-diketones and acyloins are reduced to vicinal diols.325 Enantioselectivities in the reduction of acetophenone, catalysed by 1,3,2-oxazaborolidones, have been examined using the AM1-SCF MO method. The optimized geometries, thermal enthalpies, and entropies of R and S transition states in the stereo-controlling steps of the reduction have been obtained.326... 

In the laboratory of Y. Takemoto, the asymmetric total synthesis of the marine metabolite, halicholactone was accomplished. One advanced intermediate contained a 1,2-vicinal diol moiety which was cleaved under mild conditions to afford the corresponding aldehyde. The Criegee oxidation was chosen to effect this transformation at low temperature, followed by the stereoselective allylation of the resulting aldehyde with tetraallyltin. 

NaBiO3 has been used in the oxidation of alcohols, phenols, and olefins. Allylic and benzylic alcohols are oxidized by NaBiOs to f/,/furisalurated and aromatic aldehydes, respectively [260]. In aqueous H3PO4 or AcOH, NaBiO3 cleaves the C-C bond of vicinal diols to give two molecules of carbonyl compounds (Scheme 14.121) [261]. When treated with NaBiO3 in aqueous AcOH, 2-hydroxycyclohexanone is converted to 6-oxohexanoic acid (Scheme 14.122) [262]. 

The presence of the anfi-vicinal diol unit in the phytosphingosine 67 strongly suggests the application of the double diastereocontrolled AD to the Z-alkene 64 (Scheme 25). However, in order to access the desired product 64, the mismatched diol should be obtained. Horikawa and coworkers studied both the achiral and the chiral dihydroxylation of the optically active (E)- and (Z)-allylic... 

The (S)-lactone acid 1, obtained from L-glutamic acid by nitrous acid deamination, was converted to the acid chloride, then treated with excess diazomethane followed by hydrogen iodide to yield the keto-lactone 2. Amidation occurred quantitatively to give the partially racemized amide 3, which was purified by repeated recrystallizations. The vicinal diol resulting from reaction with excess methylmagnesium iodide was protected as the acetonide 4. An isomeric mixture of olefins (Z , 26 74) was obtained from the subsequent Wittig reaction. Reduction followed by separation on silver nitrate coated silica gel gave the (Z)-and ( )-alcohols in 20% (6) and 61% (5) yield, respectively. Conversion of the (S)-( )-alcohol (5) to the chloride then afforded the thioether (7) on reaction with sodium phenylsulfide. The thio ether anion was formed by treatment with n-butyllithium. Alkylation with the allylic chloride" (8), followed by removal of sulfur, then yielded the diene 9, which was converted in several steps to (/ ) (-t-)-10,11 -epoxy famesol. 

Formal total synthesis of uvaricin was achieved by applying double cyclization of vicinal diol bis(allylic acetate) to afford bis-THF core selectively using chiral ligand Trost L-1 as a key reaction [72], Thus the cyclization of 185 afforded the diene 186 with two new stereocenters in 97 % yield as a single diastereomer. 

Finally, Kibayashi used aqueous versions of the intramolecular acyl-nitroso Diels-Alder reaction to good effect in his stereocontrolled syntheses of (-)-swainsonine (6.28) [78] and (-)-pumiliotoxin C (6.34) [79] (Schemes 1.13 and 1.14). In each case, oxazinolactam cycloadducts (cf. 6.32 and 6.38) served as key functional chiral building blocks for the remaining synthetic operations. For example, retrosynthetic analysis of the trihydroxy-indohzidine system of swainsonine (6.28) reveals that the pyrrolidine ring of this target can be formed by amine alkylation (cf. 6.29) while the vicinal diol can be installed via substrate-controlled cw-hydroxylation of a (Z)-allyl... 

The uses of the versatile oxidant pyridinium chlorochromate have been reviewed. Pyridinium chlorochromate has been used for the oxidation of methyl 5-hydroxypentanoate to the aldehyde, an intermediate useful in the synthesis of leukotrienes, and the same reagent oxidatively cleaves secondary vicinal diols to the corresponding aldehydes. The reactivity of the chlorochromate ion as an oxidant can be influenced by the counter-ion. For example, the 4-dimethylaminopyridinium salt is a mild, selective reagent for the oxidation of allylic and benzylic alcohols. Pyridinium fluorochromate oxidizes primary and secondary alcohols to aldehydes and ketones respectively in dichloromethane solution, and shows a less pronounced acidity compared with the chloro-... 

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