1.4- Diol derivatives, formation

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

The location of the position of double bonds in alkenes or similar compounds is a difficult process when only very small amounts of sample are available [712,713]. Hass spectrometry is often unsuited for this purpose unless the position of the double bond is fixed by derivatization. Oxidation of the double bond to either an ozonide or cis-diol, or formation of a methoxy or epoxide derivative, can be carried out on micrograms to nanograms of sample [713-716]. Single peaks can be trapped in a cooled section of a capillary tube and derivatized within the trap for reinjection. Ozonolysis is simple to carry out and occurs sufficiently rapidly that reaction temperatures of -70 C are common [436,705,707,713-717]. Several micro-ozonolysis. apparatuses are commercially available or can be readily assembled in the laboratory using standard equipment and a Tesla coil (vacuum tester) to generate the ozone. Reaction yields of ozonolysis products are typically 70 to 95t, although structures such as... 

Fig. 11. Mechanism for formation of parabanic acids from the methylated uric acid-4,5-diol derived from theobromine (3,7-dimethylxanthine) and caffeine (1,3,7-trimethylxan-thine). Molar amounts of products are those formed in 1 M HOAc...

To model the photochemical reaction of Re2(CO)io with silica in the presence of THE, silanolates other than silsesquioxanes [Et3SiOH, PhsSiOH, Ph2Si(OH)2 and (OH)Ph2SiOSiPh2(OH)j with [Re2(CO)8(THE)2] have also been synthesized [148], pointing to the formation of the surface species [((r-=SiO)((r-H)Re2(CO)8j in the above-mentioned reaction with silica. Rhenium carbonyl of the two diol derivatives listed above where both the SiOH have reacted are proposed as models for surface reaction with a vicinal hydroxyl residue, although no direct surface species is reported [148]. 

Diastereomeric 1,3-amino alcohols 1 have been obtained by reduction of 4,5-dihydroisoxa-zoles350-353. 3C chemical shifts allow a stereochemical differentiation due to the formation of energetically preferred chelated conformations. Similar to /3-hydroxy carbonyl compounds and 1,3-diol derivatives, the chemical shifts of the backbone carbons are larger in the syn 1,3-amino alcohols than in the awn -isomers353. 

Charette and coworkers have shown that the diastereoselective cyclopropanation of chiral allylic alcohols with gem-dizinc carbenoids proceeds with high diastereocontrol for protected 2-butene-1,4-diol derivatives (equation 63). The minimization of the A-1,3 strain and the formation of a zinc chelate in the product is believed to be responsible for... 

The fluorescence In dilute solution is measured for five polyesters with terephthalate as the rigid aromatic unit and diols derived from cyclohexane as the flexible spacer, A conformational analysis concludes that the spacers most conducive to excimer formation are the 1,3-c/s-cyclohexanediol and 1,4-e/s-eyclohexanedimethanol. This result from calculations is compatible with experimental results. 

Reactions. Experimental results of reactions of (Tip)2 Si= Si(Tip) Si(Tip)=Si(Tip)2 are summarized in Scheme 40. Treatment of the tetrasilabutadiene with a small amount of water gave an analog of tetrahydrolhran, an oxatetrasilolane derivative, probably via the 1,2-addition and the following rearrangement. Addition of an excess amount of water resulted in the formation of the tetrasila-l,4-diol derivative, which showed no tendency to ehminate water with the formation of the oxatetrasilolane derivative. 

When l,l,2-triphenylethane-l,2-diol-derived esters are submitted to a monodeprotonation and subsequently treated with Chlorotrimethylsilane, the formation of 2-trimethylsilyloxy-l,3-dioxolanes results. The orthoester moiety thus obtained serves as a protecting group for carboxylic acids (eq 3) it is stable towards alkyllithium reagents and can be cleaved under nonacidic conditions by alkaline hydrolysis. ... 

Marshall has proposed transition state 422 to rationalize the formation of the major anti diol derivatives (Eq. (11.38)). The minor syn diol adduct 418 is thought to arise via the (Z)-y-alkoxyindium intermediate 423 by way of transition state 424 (Eq. (11.39)) [171]. 

A number of investigations have explored the reactions of ally lie stannanes containing a y-alkoxy substituent. A direct preparation of these substances utilizes the kinetic deprotonation of an allyl ether followed by alkylation with tri-n-butylstannyl chloride. In a typical experiment, the deprotonation of 101 with 5-butyllithium leads to internal coordination of lithium cation and provides formation of the Z-allylstannane 102. The behavior of y-alkoxyallylstannanes is similar to the corresponding Z-alkylstannanes, and as a result, the reaction provides a stereoselective route for the synthesis of complex diol derivatives. In the allylation of chiral aldehyde 80 with stannane 102, /l-chelation dictates face selectivity. The expected. yyn, anti-product 104 is obtained with high diastereoselection via the antiperi-planar 103, which accommodates the sterically demanding silyl (TBS) ether (Scheme 5.2.23).23... 

Additional examples, shown in Scheme 5.2.25, illustrate a-chelation control in the formation of 111 and 114,36 37 as well as the inclusion of chirality in the y-alkoxy substituent in 115 leading to 116,3 a role for coordination in the case of the a-amido substituent of 118, which yields selective formation of diol derivative 119 via 121.39... 

Two almost simultaneous communications reported the successful syntheses of a-cedrene (123) and cedrol (124). Both syntheses were modelled along a proposed biogenetic scheme, and as such the penultimate goal was the generation of the cation (125) which should, and did, undergo a smooth acid-catalysed cyclisa-tion to a-cedrene. The two pathways to this cation differed in several respects yet practically coincided at the key spiro-dienone ester (126, R = Me and R = Et ). Whereas Crandall and Lawton completed the synthesis by formic acid treatment of the alcohol (127), Corey et al. found that similar treatment of the diol (128) also yielded a-cedrene, albeit in lower yield. Alternatively, the ene-diol (129) was converted into a-cedrene in better yield by formic acid treatment, thermolysis of the derived formates and subsequent lithium-ethylamine reduction of the diene (130). Finally, cedrol (124) was obtained by boron trifluoride cyclisation of the enol-acetate (131), followed by methyl-lithium treatment of the intermediate cedrone. 

An interesting synthetic target related to triptindane is the tris(naph-tho)[3.3.3]propellane 86 (Schemes 16 and 17). Alder et al. [84] reported on first attempts to construct this two-fold triptindane bearing a highly strained C - C bond. Cyclodehydration of acenaphthenediol 85, prepared previously from acenaphthene quinone (84) [85], or the corresponding pinacolone formed as an intermediate in the acidic medium, did not occur in the desired way (Scheme 16). Attempts to utilize the corresponding bis(dihydro) derivative (i.e. the diol derived from 87) resulted in the formation of the C2-symmetrical polycycle 88, possibly by di-oxy Cope rearrangement followed by a criss-cross [2 + 2] cycloaddition [84]. 

PAHs are ubiquitous environmental pollutants known to be mutagenic and carcinogenic in mammalian cells [131, 132]. PAHs require metabolic activation that results in diol epoxide formation via reactions that are catalyzed by epoxide hydrolase and the CYP450 family of enzymes [133], Diol epoxides are highly reactive, particularly toward purines in DNA, forming guanine and adenine adducts that exist as as and trans stereoisomers [134]. Transcription past adducts derived from diol epoxides of benzo[o]pyrene (benzo[a]pyrene diol expoxide (B[a]PDE)), benzo[c]phenanthrene (benzo[c]phenanthrene diol epoxide (B[c]PhDE)), and dibenzo[a,l]pyrene (dibenzo[o,l]pyrene diol epoxide (B[a,l]PDE)) has been studied. 

In an attempt to characterize the active catalyst from chiral diols derived from tartrate and dichlo-ro(diisopropoxy)titanium, by NMR analysis, incomplete catalyst formation and chiral, as well as achiral, titanium complexes were observed. The ratio of chiral diol incorporation into the catalyst is enhanced by the addition of molecular siex es and therefore the enantioselectivity is increased31. 

The methods described in the preceding section lead to smooth phosphorylation of all hydroxyl groups in inositol derivatives. Contrary to this exhaustive phosphorylation, the regioselective one is also quite useful, especially for the selective formation of the phosphoric diester functions at the C-l position in 1,2-diol derivatives of myo-inositol in the synthesis of phosphoinositides. These 1,2-diol derivatives are easily accessible because 1,2-cis-dihydroxyl groups of myo-inositol are easily protected by its ketalization in comparison with trans diols. The diol derivatives thus obtained comprise one equatorial and the other axial hydroxyl groups. Since the former is generally more reactive than the latter, several electrophiles were selectively introduced at the 1 position of the diols as shown in Scheme 2-5. However, phosphorylation at C-1 in a 1,2-diol was extraordinarily difficult when known procedures were used because migration of the phosphate function and cyclization occured with ease.- ... 

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