1.2- Propanediol, 1,2-diphenyl

The pinacol rearrangement is frequently observed when geminal diols react with acid. The stmcture of the products from unsymmetrical diols can be predicted on the basis of ease of carbocation formation. For example, l,l-diphenyl-2-metltyl-l,2-propanediol rearranges to... 

Boro nophenyl) alanine (BPA) is a practical boron compound which is clinically used for the treatment of not only malignant melanoma but also of brain tumors, in neutron capture therapy (Scheme 1-40) [105, 152, 153]. Although (pinacolato)di-boron (82) is an excellent reagent to afford the corresponding boronate in 88% yield, it strongly resists the hydrolysis to arylboronic acids. Alternatively, the 1,3-diphenyl-propanediol ester (85) is more convenient to deprotect the diol moiety by catalytic hydrogenolysis [105]. 

Lipase CA catalyzed the polymerization of cyclic dicarbonates, cyclobis (hexamethylene carbonate) and cyclobis(diethylene glycol carbonate) to give the corresponding polycarbonates [105]. The enzymatic copolymerization of cyclobis(diethylene glycol carbonate) with DDL produced a random ester-carbonate copolymer. As to enzymatic synthesis of polycarbonates, reported were polycondensations of 1,3-propanediol divinyl dicarbonate with 1,3-propanediol [110], and of diphenyl carbonate with bisphenol-A [111]. 

Kagan and coworkers studied the reaction between cyclopentadiene and 310 in the presence of aluminum alcoholates of chiral diols and their chiral mono ethers208. Among the various diols studied, only 1,1-diphenyl-1,2-propanediol (325) gave satisfactory results. Optimization by variation of the dienophile/catalyst ratio, aging of the catalyst and variation of the temperature ultimately resulted in a maximum of 86% ee at —100 °C. 

Problem 14.59 Outline the steps and give the product of pinacol rearrangement of (a) 3-phenyl-l,2-propanediol, (b) 2,3-diphenyl-2,3-butanediol. ... 

J. F. Duncan and K. R. Lynn, J. Chem. Soc., 3512, 3519 (1956) J. B. Ley and C. A. Vernon, Chem. Ini. (London), 146 (1956).] That the rate-determining step can be the migration when the first-formed carbocation is particularly stable has been shown by Schubert and LeFevre [note 18(b)]. These workers subjected 1,1-diphenyl-2-methyl- 1,2-propanediol to the pinacol rearrangement and found that deuterium substitution in the migrating methyls caused the reaction to slow down. 

Hydrogenation of ethyl 2,4-dioxopentanoate with an (S)-MeO-BIPHEP-Ru complex followed by in situ cyclization gives (3R,5S)-3-hydroxy-5-methyltetrahydrofuran-2-one with 98% ee and the 3R,5R isomer with 87% ee in an 84 16 ratio [236]. Ethyl 2-hydroxy-4-oxopentanoate is the only detectable intermediate. 1,3-Diphenyl-l,3-propanediol with a BIPHEMP-Ru complex is transformed to an anti-diol selectively [237]. 1,5-Dichloro-2,4-pentanediol, a versatile chiral building block, is selectively obtained through the BINAP-Ru catalyzed hydrogenation of a... 

Recently, a series of studies of the stereoselective reduction of 1,3-diketones has been reported which expands upon this methodology. When 1,3-diphenyl-1,3-propanedione was reduced with three equivalents of NaBH4 in the presence of (S,S)-15,THFA,and ethanol in CHCI3 at -20°C, (S,S)- 1,3-diphenyl- 1,3-propanediol was obtained quantitatively in 97% ee (Scheme 9) [54], The anti syn ratio of the product was 84 16. Diketones with electron-donating and electron-withdrawing substituents on their phenyl rings were also reduced with high enanti-oselectivity and diastereoselectivity. 

The impure lactone of 1-hydrozyoyoIohexaneaoetio acid and that of 2,2-dim thyl-8-phenyl hydracirylio acid react in the same way to give l-hydrozycydohexane-ethanol and 2-methyl-l-phenyl-1,2-propane-dlol respectively. The lactone of 2,2-diphenylhydracrylic acid, which ie crowded, does not react with metbylmagnesium iodide, but is reduced by lithium aluminum hydride to 2,2-diphenyl-1,3-propanediol with a yidd of S4%. 

ProMem 28.11 Give the structure of the carbonium ion generated (a) by action of acid on 1,1-diphenyl-1,2-propanediol (b) by action of nitrous acid on l.t-diphenyl-2-amino-1 -propanol. 

Methyl-l,l-diphenyl-1,2-propanediol (50 g) is added with stirring to concentrated sulfuric acid (300 ml) at 5°. The mixture is left at room temperature for 2 h, then poured on ice and diluted with water (to 3 1) the precipitated 3,3-diphenyl-2-butanone is distilled in a vacuum, then having b.p. 101-103°/0.3 mm and m.p. 40-41° (38 g). 

Write the condensed structural formula for each of the following compounds (a) 2-pentanol, (b) 1,2-propanediol, (c) ethyl acetate, (d) diphenyl ketone, (e) methyl ethyl ether. 

Diphenyl methane diisocynate, 1,6-hexamethylene diisocyanate and polyoxypropylenediol 3-Chloro-l,2 propanediol or 1,2-propanediol - [57]... 

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