1,2-Diols reduction

Iodates by ene-diols, reduction of. . Isomerization of tetra-O-acetyl-2-... 

Under other conditions, reduction leads to diols. Reductive coupling to diols can be done using magnesium amalgam248 or zinc dust.249... 

In the synthesis of fluorinated analogs of the acetylcholinesterase inhibitor, huperzine A, it was necessary to accomplish reductive elimination of the diol 15-D to 15-E. Of the methods for diol reduction, which seems most compatible with the other functional groups in this compound ... 

Intramolecular coupling Some aromatic diketones have been stereoselectively cy-clized under various electrolysis conditions, which, together with the substrate structure, strongly influence the stereochemistry of the formed cyclic diol. Reductive cyclization of 1,8-diaroylnaphthalenes led to trans-diols, 2,2 -diaroylbiphenyls and a, )-diaroylalkanes yielded cis-diols with different stereoselectivities depending on substrate structure and electrolysis conditions (pH, cosolvent) (Fig. 57) [310-312]. 

This cycloaddition-reduction-hydrolysis sequence was also used in an approach to butyrolactones related to ribonolactone (71). These compounds are inducing agents of hunger and satiety in mammalians. Here, a subsequent aldol 1,3-diol reduction was used, and the required carboxy function was established by oxidation of the aromatic ring with ruthenium tetroxide. Cycloaddition of benzonitrile oxide to allyl alcohol afforded an enantiomeric mixture of isoxazolines 55 and 56, which were treated with sodium hydride and methyl iodide to achieve separation by chromatography on cellulose triacetate (71). 0-Demethylation, followed by... 

Enantiomerically pure compound was obtained by recrystallization of the corresponding p-nitrobenzoyl ester 36 in 78% yield. After hydrolysis, selective protection of the diol, reductive debenzylation using lithium di-t-butyl biphenylide (LiDBB), and TPAP-catalyzed oxidation gave aldehyde 27. 

Fig, 21. Rate of butyne-l,4-diol reduction vs. relative composition of a composite Pd and Ru catalyst (after Rylander and Cohn, 40). 

Other workers have concentrated on the introduction of functionality into ring C of tabersonine (78). Danieli et al. (252) introduced the 17-hydroxy group by oxidation of tabersonine by means of phenylseleninic anhydride. Presumably, the Va,17-didehydrotabersonine initially produced suffers nucleophilic attack by water during workup, the stereochemistry of attack being controlled by the adjacent ethyl group. Oxidation of the product, 377, at C-16 by means of peracid also proceeds preferentially at the /3-face to give the V-oxide 378 of the desired diol. Reductive methylation and acetylation then complete the partial synthesis of vindorosine (43) (Scheme 24) (252). 

Storage Moisture-sensitive store in cool, dry place away from heat, sparks, open flame store under nitrogen keep tigthly closed Uses Reducing agent in silylation-reduction-allylation sequence of p-hydroxy esters to homoallylic-substituted 1,3-diols, in silylation-hydrosilation-oxidation of allyl alcohols to 1,3-diols, reduction of p-hydroxy ketones to anti-1,3 diols... 

Haley and coworkers simplified and expanded the scope of available fully conjugated indeno[l,2-fe]fluorenes in a subsequent report (Scheme 2.20) [69]. Easily accessible indeno[l,2-fe]fluorene-6,12-diones 33 were prepared in three steps. Then, addition of (triisopropylsilyl)ethynyllithium and an acidic work-up provides the diols. Reduction with SnCl2 in toluene yields fully conjugated derivatives of 28. The compounds were shown to reversibly accept two electrons... 

Single diastereomers of the diol products were obtained by a two-step process after careful selection of the biocatalysts. In the first reduction step, the starting substrate was completely converted into the corresponding P-hydroxy ketone by the first KRED enzyme without any further reduction to the 1,3-diol. Reduction reactions were coupled with the glucose/glucose dehydrogenase (GDH) system for the in situ regeneration of the reduced cofactor. The second KRED enzyme was then added to... 

DMSO can be boiled under reflux for long periods largely unchanged (3.7% of volatile decomposition products after 72 h) but under air or O2 in a sealed tube, kept just below the boiling point (189 C) for 68 h, it is completely transformed into paraformaldehyde, dimethyl sulphide, and bis(methylthio)methane, water, and dimethyl disulphide." " Peroxides catalyse the decomposition, as does MeSOjH." " The formaldehyde formed in this way can be used for in situ methylene acetal formation with oxidation products of alcohols and diols." Reduction of DMSO with Br2+HBr gives MezS, MeSOsH, and paraformaldehyde, while diphenyl sulphoxide is unchanged." ... 

As mentioned briefly in Section 7.3.2, a spin-off application of the diol reduction has been the citrate or DMF reductions in the presence of PVP at an elevated temperature [31, 68, 70], When citrate ion in aqueous solution is used in the reduction of gold precursors, a mass production of triangular nanoplates was realized. It was also shown that the nanoplate could be further fabricated, by using fast ion bombardment (FIB), into a future component of a possible nanomachine, such as a nanometer-sized gear element [31]. As more PVP was added the width and thickness of the nanoplates increased monotonically this contrasted with the polyol process, where smaller crystals were formed as the molar ratio of PVP increased... 

C21H36O2. M,p. 238°C. There are four isomeric pregnane-3,20-diols differing only in the orientation of the hydroxyl groups at positions 3 and 20 and with the 5/ configuration. Only the 3a,20a occurs naturally. It is formed by reduction of progesterone in the liver and is the chief urinary metabolite of it, being... 

Symmetrical diols can be made by a radical reaction. Radical reactions are rarely much use in carbon-carbon bond formation as they often give poor yields and many products They are of course useful in some FGl reactions in things hke altylic bromination and in functionahsing remote carbon atoms. If rou want to read more about this see Tedder, Part 2, Chapter 11 or Carruthers, Chapter 4. One useful radical reaction is the prnacol reduction ... 

To illustrate how aldol condensation may be coupled to functional group modifi cation consider the synthesis of 2 ethyl 1 3 hexanediol a compound used as an insect repellent This 1 3 diol is prepared by reduction of the aldol addition product of butanal... 

Reduction. Hydrogenation of dimethyl adipate over Raney-promoted copper chromite at 200°C and 10 MPa produces 1,6-hexanediol [629-11-8], an important chemical intermediate (32). Promoted cobalt catalysts (33) and nickel catalysts (34) are examples of other patented processes for this reaction. An eadier process, which is no longer in use, for the manufacture of the 1,6-hexanediamine from adipic acid involved hydrogenation of the acid (as its ester) to the diol, followed by ammonolysis to the diamine (35). 

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