Reduction trimethyl phosphite

The reduction of keto steroids by treatment with chloroiridic acid, or sodium chloroiridate, and trimethyl phosphite has been studied in some detail.Ketones at the 2- and 3-positions are reduced predominantly to the corresponding axial alcohols, while ketones at 4,6,7,11,12,17 and 20 are not affected. The rate of reaction is increased by addition of aqueous sodium hydroxide. Replacement of sodium chloroiridate by tris(triphenylphos-phine)rhodium chloride gives a system which reduces a 3-keto steroid to the... 

A mixture of the ketone (4.62 g), iridium tetrachloride (1.23 g), trimethyl phosphite (15 ml), propan-2-oI (200 ml) and water (50 ml) is heated under reflux for 21 hr. Much of the solvent is then distilled off ca. 215 ml) and the organic products remaining are isolated by extraction with ether. If reduction is essentially complete, the product at this stage may be sufficiently pure for most preparative purposes. Pure components can be obtained by chromatography over alumina, a representative experiment (on the above scale) gives unchanged ketone (0.13 g), cw-alcohol (4.36 g) and tmns-2 co o (0.16 g) (eluted in this order by pentane, and then by pentane containing ether). 

Heating 3,4-bis(phenylsulfonyl)furoxan with a solution of sodium butoxide in butanol followed by reduction with trimethyl phosphite gives furazan 281 (Scheme 183). Compound 281 was converted into dialkoxy derivative 282 with the lithium salt of ( )-l-azabicyclo[2.2.2]octan-3-ol in 33% overall yield (96W012711, 97EUP773021, 98JMC379). 

The present method is based on the earlier described ozonolysis of phenanthrene in methanol. The reduction of the peroxidic reaction mixture with trimethyl phosphite to give diphenaldehyde, isolated as the di- -nitrophenylhydrazone, in quantitative yield has been described recently.10 The disadvantage of this method is that the dialdehyde cannot be isolated in the free state in high yield. Diphenaldehyde has also been obtained by sodium... 

This is, as expected, the rarest oxidation state as far as non-organometallic complexes of rhenium are concerned. The dirhenium phosphite complex Re2[P(OMe)3]10 has been prepared12,13 in low yield by several methods, viz. the potassium-potassium iodide reduction of ReOCl3(py)2 or an ReCLj-pyridine complex, followed by treatment with trimethyl phosphite. This yellow complex displays a 31P H) NMR spectrum that appears as a first order AB4 pattern, and is isoelectronic with Re2(CO)l0. It reacts with H2 upon photolysis in THF solution to produce hydridorhenium(III) and other species.13 The related triphenyl phosphite derivative Re2[P(OPh)3]l0 has been described14 as a product of the reaction between ReH3(PPh3)4 and P(OPh)3. 

Iodine is liberated quantitatively from acidic iodide solution by 84 and 86.71-72 Reduction of the cyclic diphenoyl peroxide (86) with triphenylphosphine or trimethyl phosphite leads to an 80% yield of... 

Deoxygenation of a nitrone. Some years ago Todd and co-workers noted that 1-pyrroline-1-oxides can be obtained by reductive cyclization of a y-nitro ketone. This reaction was used recently in a synthesis of chlonns related to vitamin B,. Thus the nitro ketone 1 on reduction with zinc and acetic acid gives the pyrroline N-oxide 2 in high yield. The N-oxide is stable to triphenylphosphiue or trimethyl phosphite, but is reduced to the imine 3 in high yield by TiCl,. 

Henbest redmetkm. Reduction of the ketone (I) with chloroiridic acid and trimethyl phosphite resulted in a 73 % yield of the axial 3 -alcohol (2). Sodium borohydride... 

Ozonides are rarely isolated [75, 76, 77, 78, 79], These substances tend to decompose, sometimes violently, on heating and must, therefore, be handled with utmost safety precautions (safety goggles or face shield, protective shield, and work in the hood). In most instances, ozonides are worked up in the same solutions in which they have been prepared. Depending on the desired final products, ozonide cleavage is done by reductive or oxidative methods. Reductions of ozonides to aldehydes are performed by catalytic hydrogenation over palladium on carbon or other supports [80, 81, 82, S3], platinum oxide [84], or Raney nickel [S5] and often by reduction with zinc in acetic acid [72, 81, 86, 87], Other reducing agents are tri-phenylphosphine [SS], trimethyl phosphite [89], dimethyl sulfide (DMS) [90, 91, 92], and sodium iodide [93], Lithium aluminum hydride [94, 95] and sodium borohydride [95, 96] convert ozonides into alcohols. 

The di-O-tosylates (prepared by action of tosyl chloride in pyridine) are reduced with zinc (Nal/Zn route e Tipson-Cohen reaction) [13]. Cyclic ortho-esters (prepared by reaction of the diol with ethyl orthoformate) are transformed into olefins by simple heating in the presence of acids (Eastwood reaction, route b) [14]. Cyclic thiocarbonates (obtained by reaction of a diol with thiophosgene or (V,(V -thiocarbonyl-di-imidazole) are reduced to olefin with trimethyl phosphite (Corey-Winter method, route c) [15]. Finally, reduction of vicinal di-xanthates with tri- -butyltin hydride according to the Barton procedure [16] affords olefins via a reductive elimination process route a). The Corey-Winter, Garegg, and Tipson-Cohen methods are most commonly applied for deoxygenation of sugar diols. 

Henbest et al. used this reagent as catalyst in combination with aqueous isopropanol and trimethyl phosphite for the reduction of ketones the reaction mixture is refluxed for 1-5 days. The main reducing agent is the trivalent phosphorus species a little of the isopropanol is converted into acetone. The trimethyl phosphite... 

As noted (1, 132), an early procedure of Eliel and Doyle for the reduction of 4-t-butylcyclohexanone to cis-4-f-butylcyclohexanol used iridium trichloride supplied by Fisher. This reagent is no longer available and, in a newer procedure,1 iridium tetrachloride is used as catalyst in combination with trimethyl phosphite, which undergoes hydrolysis to phosphorous acid the actual reducing agent is probably... 

Chloroiridic acid and iridium trichloride [1, 131-132, before references], Henbest et al. introduced chloroiridic acid as catalyst, in combination with aqueous isopropanol and trimethyl phosphite, for reduction of a ketone to form a high proportion of an axial alcohol. For reduction of 4-t-butylcyclohexanone to the cA-alcohol, Eliel and Doyle2 used iridium trichloride with initially favorable results (as noted,... 

The chloroiridic acid and trimethyl phosphite system in 90% aqueous isopropanol is completely selective for reduction of 3-oxo-functions of steroids, in the presence of unprotected oxo-groups at any of the other skeletal positions where they are commonly found in natural steroids (C-6, C-11, C-12, C-17, and C-20) ... 

Tris(triphenylphosphine)RhCl associated with trimethyl phosphite in isopropanol gives even greater selectivity (100%) of the axial alcohol. Reductions are conveniently effected (24 h at 82°C) in a sealed tube. The reducing agent approaches from the less hindered side of the carbonyl and the mechanism does not proceed via the hydrogenation of an enol. 

Reduction of a 1,6-diketone with trimethyl phosphite followed by cyclization in the boiling solvent is a method which has been used by several workers to synthesize cephalosporin-type antibiotics. In this example, the diketone is prepared in situ by ozonolysis on an alkene side-chain. 

Investigations of the Henbest reduction of ketones using chloroiridic acid and trimethyl phosphite in aqueous propan-2-ol have shown that the reduction is specific for 3-ketones in both the 5a- and 5 -series in the presence of 4-, 6-,... 

The thermally labile intermediate 4 could also be isolated (and was characterised by X-ray analysis ) when the reaction was performed in the presence of trimethyl phosphite L in place of carbon monoxide. As a consequence, the metal becomes more electron-rich and reductive elimination does not occur. With the structure of 4 being firmly established, the pathway shown in Scheme 1 was proposed and it was realised that the Fe-N=C fragment resembles a bS-dipole." By labelling studies and from the X-ray structure of 4 with L = P(OMe)3... 

Barton has devised such a pathway for converting carboxylic acids to hydroperoxides via A -hydroxypyridine-2-thione esters [16a,b] (Scheme 5). The yields of hydroperoxides are 45-89% [16]. Reduction of the crude products with trimethyl phosphite (rt) or dimethyl sulfide (80 °C) readily provides the corresponding alcohols. On the other hand, tosylation and ensuing Kornblum-De La Mare type fragmentation [17] leads to carbonyl compounds [16b] (Scheme 5). 

Furthermore, treatment of the crude mixture of azido alcohols 152 and 153, obtained by azidolysis of tosylate precursors, afforded aziridine 154 in high yield. Danishefsky and coworkers reported that reductive cyclization of an exocyclic azido mesylate in the presence of trimethyl phosphite, followed by... 

The reduction of trimethyl phosphite-borane by sodium naphthalide produces a new type of diphosphine derivative. The isomer which apparently explains all of the observed properties of the compound is (21). ... 

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