Configuration from diols

In order to prove the utility of this method and to ascertain the absolute configuration of the products, (S)-alanine has been enantioselectively prepared. The key step is the addition of methyllithium to the AjA -dimethyl hydrazone acetal 4c, derived from diol 3c. In accordance with 13C-NMR investigations it can therefore be assumed that all major diastereomers resulting from the addition of organolithium reagents to hydrazone acetals 4a-c derived from diols 3a, 3b or 3c (Table 3, entries 1 -6) have an S configuration at the newly formed stereogenic center. 

Dimethylaminobenzoates have also been used to establish the absolute configuration of diols in the presence of an aromatic chromophore, including metabolites of benzo[a]pyrene163 and precocene I164, as well as the cis-dihydrodiol derived from 12-methylbenz[a]anthracene165 and diastereomeric 2,2 -spirobiindane-l,l -diols166. 

The origins of two chirality rules, the Octant Rule for ketones and the Exciton Chirality Rule, have been explained, and it has been shown how the rules can be applied to the determination of molecular absolute configuration. In applications of the Octant Rule, when the absolute configuration of a ketone is known, the rule may be used to determine its conformation. Applications of the Exciton Chirality Rule to determine the absolute configuration of diols follows from the derivatization with strongly UV-visible absorbing chromophores. 

The rate of oxidation of diols with lead tetraacetate depends strongly on their configurations cis diols react 200-3000 times faster than trans diols [1154], and the racemates of certain diols react about 15 times faster than the meso forms [1154]. The rates of oxidation of pinacols prepared from cyclopentanone, cyclohexanone, and cycloheptanone are in the ratio... 

Conversion of 971 to epoxide 973 via mesylate 972 results in inversion of the configuration at C-3 due to an Sn2 reaction. Transformation of the olefin to an acid followed by lactoni-zation results in a second inversion, this time at C-2, producing diastereomer 975. If no inversion reactions are performed, the third diastereomer 983 can be obtained from diol 979 as shown in Scheme 133. 

Double bonds can be oxidised to vicinal diols by a variety of reagents of which the most useful are alkaline potassium permanganate and osmium tetroxide. With both reagents, c/s-addition occurs to yield diols of the erythro configuration from c/s-double bonds, and diols of the threo configuration from frans-double bonds. The following procedure utilises alkaline permanganate and is particularly suited to reaction with monoenes and dienes [671],... 

Cyclic Dienes - A number of optically active tricarbonyl iron ic-complexes with unsymmetrical cyclohexadiene and cyclohexadienyl ligands have been prepared from diols available by the oxidation of arenes by Pseudomonas putida. The circular dichroism spectra of the metal complexes were shown to provide an empirical guide for the assignment of absolute configuration from chiroptical data for this class of compounds. 

The addition of acetylides to oxiranes yields 3-alkyn-l-ols (F. Sondheimer, 1950 M.A. Adams, 1979 R.M. Carlson, 1974, 1975 K. Mori, 1976). The acetylene dianion and two a -synthons can also be used. 1,4-Diols with a carbon triple bond in between are formed from two carbonyl compounds (V. Jager, 1977, see p. 52). The triple bond can be either converted to a CIS- or frans-configurated double bond (M.A. Adams, 1979) or be hydrated to give a ketone (see pp. 52, 57, 131). 

Acetonides are the most suitable base-stable protecting group for 16,17-cis-diols. They can be readily prepared from 16,17-disecondary alcohols with either the a- or j5-configurations. ... 

The C2-symmetric epoxide 23 (Scheme 7) reacts smoothly with carbon nucleophiles. For example, treatment of 23 with lithium dimethylcuprate proceeds with inversion of configuration, resulting in the formation of alcohol 28. An important consequence of the C2 symmetry of 23 is that the attack of the organometallic reagent upon either one of the two epoxide carbons produces the same product. After simultaneous hydrogenolysis of the two benzyl ethers in 28, protection of the 1,2-diol as an acetonide ring can be easily achieved by the use of 2,2-dimethoxypropane and camphor-sulfonic acid (CSA). It is necessary to briefly expose the crude product from the latter reaction to methanol and CSA so that the mixed acyclic ketal can be cleaved (see 29—>30). Oxidation of alcohol 30 with pyridinium chlorochromate (PCC) provides alde-... 

Diisopropylamino(dimethyl)silyl]-2-propenyl]lithium adds to aromatic and x-branched aldehydes in the presence of anhydrous zinc chloride with essentially complete anti stereoselectiv-ity3s. as expected from the chair-like pericyclic transition state formed by the ( -intermediate. The addition products are not isolated, but after O-silylation, oxidative desilylation with retention of configuration forms the rmft-diols. 

Initial attack by base on (34) yields the alkoxide anion (36), internal attack by this ROe then yields the epoxide (37) with inversion of configuration at C (these cyclic intermediates can actually be isolated in many cases) this carbon atomf, in turn, undergoes ordinary SN2 attack by eOH, with a second inversion of configuration at C. Finally, this second alkoxide anion (38) abstracts a proton from the solvent to yield the product 1,2-diol (35) with the same configuration as the starting material (34). This apparent retention of configuration has, however, been brought about by two successive inversions. 

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