Diols cyclic

For cyclic 1,2-diol-Cr(V) complexes, the multiplicity of the room-temperature CW-EPR signal depends upon the cyclic strain in the ligand.50 For these systems, the observed EPR hyperfrne pattern of the Cr(V)-diolate2 formed by reduction of Cr(VI) with GSH in the presence of c/.v-1.2-cyclohexanediol (6) or trans-1,2-cv c I oh e x an ed i ol... 

Intramolecular coupling to cyclic 1,2-diols and its synthetic applications... 

The ease of formation of alcoholates and adducts can be related to both the acidity and the geometry of the poly hydroxy compound. The geometry is important, in that the chelate ring must possess a minimum of strain in order to allow the complex to possess the maximum stability. Reaction of a cyclic 1,2-diol with a metal hydroxide is physically impossible if the hydroxyl groups are oriented in directions that are exactly opposite (180°) to each other. Cyclic 1,3-diols can form chelates if both of the hydroxyl groups are cis and axial. An example of this is the reaction of 1,6-anhydro-... 

The reaction of cyclic 1,2-diols with 1 can result in epoxides or ketones, as illustrated for the case of 3-methylcyclohexane-1,2-diols (equations I and II).2... 

Cyclic amino-carbenes, in molybdenum carbonyls, 5, 457 Cyclic bis(phosphine) dichlorides, with iron carbonyls, 6, 48 Cyclic carbenes, as gold atom ligands, 2, 289 Cyclic carbometallation, zirconium complexes, 10, 276 Cyclic carbozirconation characteristics, 10, 276 intermolecular reactions, 10, 278 intramolecular reactions, 10, 278 Cyclic dinuclear ylides, and gold , 2, 276 Cyclic 1,2-diols, intramolecular coupling to, 11, 51 Cyclic enones, diastereoselective cuprate additions, 9, 515 Cyclic esters, ring-opening polymerization, via lanthanide catalysis, 4, 145 Cyclic ethers... 

Intramolecular geometries, database studies, 1, 597 Intramolecular hydroalkoxylation, and etherification, 10, 672 Intramolecular pinacol coupling to cyclic 1,2-diols, 11, 51 with samarium reagents, 11, 60 Intramolecular silylformylation, alkynes and alkenes, 11, 489 Intramolecular solvomercuration alkenes, 2, 436 alkynes, 2, 439... 

Intramolecular pinacol coupling reactions are known, giving cyclic 1,2-diols. Dialdehydes have been cyclized by reaction with TiCls to give cyclic 1,2-diols in good yield. ° A radical-induced coupling of an a,03-dialdehyde led to cw-l,2-cyclo-pentanediol when treated with BuaSnH and AIBN. or induced photochemically. ... 

Exploration of the reduction of dicarbonyl compounds has centered on attempts to achieve intramolecular coupling of radical intermediates to give a cyclic 1,2-diol. A mechanistic study of the production of cyclopropanediols, during the reduction of 1,3-dibenzoylpropane in acetonitrile, has been made [110]. It is suggested that the ratedetermining cyclization step is the addition of the radical anion from one ketone function onto the second carbonyl group in the same molecule. 

Diols Only vicinal cw-OH groups of cyclic 1,2-diols readily form acetals. " Acetal exchange is the most common method for preparing isopropylidene acetals (1,3-dioxolanes). 

RCHOHR Alcohols — C-H cyclic 1,2-diol sulfates -OH 2.2 NaBH, - NaCNBHg... 

In analogy to intermolecular pinacolic coupling reactions, organometallic dialdehydes have served as precursors for the intramolecular version of the reaction, affording cyclic 1,2-diols [39]. Both arene chromium tricarbonyl (Eq. 29) and ferrocene complexes (Eq. 30) afford excellent yields of the desired products. 

The McMurry reaction (see Section 2.9) can allow the formation of alkenes from dicarbonyl compounds. This reaction generates an intermediate 1,2-diol (pinacol), which is converted on the surface of the titanium to the alkene. The two carbon-oxygen bonds do not break simultaneously and the reaction is not stereospecific. Thus, both anti and syn acycUc 1,2-diols give mixtures of Z- and -alkenes. With cyclic 1,2-diols, the two oxygen atoms must be able to bond to a common titanium surface. Thus, the cis-diol 45 eUnunates to the alkene 46, whereas the trans-dio 47 is inert under these reaction conditions (2.43). ... 

Oxidative Cleavage of l,2-Diols7 1,2-Diols are cleaved by Mn02 to aldehydes or ketones. With cyclic 1,2-diols, the reaction leads to dialdehydes or diketones (eqs 33 and 34) and the course of the reaction depends on the configuration of the starting material (eqs 34 and 35). ... 

Koo et al. have developed an efficient method for the preparation of diverse co-formyl-a,p-unsaturated carbonyl compounds 268 and 273 that relied on the Pb(OAc)4-promoted oxidative ring cleavage of cyclic 1,2-diols 267 and 272, respectively, which in turn can be readily obtained by the 1,2-addition of various nucleophiles to a cx -acetoxy-substituted conjugated cycloalkenones 266 and a-acetoxy cyclohexanone 271. The authors also optimized the conditions for the intramolecular MBH reactions of 268 and 273. The utility of this sequence is demonstrated by the syntheses of chromones 270 and the precursor (274) of the compound containing the 6,8-dioxabicyclo[3.2.1]octane ring (Scheme 1.98). ... 

Cyclic 1,2-diols can be produced stereoselectively from cycloalkenes. For example, a racemic mixture of the enantiomeric frflns-l,2-cyclohexanediols 7 and 8 is produced by reaction of a peracid with cyclohexene and hydrolysis of the intermediate epoxide 13 (Eq. 7.1). Oxidation of this alkene by permanganate, on the other hand, gives ds-l,2-cyclohexanediol (6), as shown in Equation 7.2. The intermediate in this process is presumably the cyclic manganese-containing species 14, which is not isolated. 

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