Epoxides reductive coupling

An unprecedented nickel-catalyzed reductive coupling between an epoxide and an alkyne to give synthetically useful homoallylic alcohols has been developed by Jamison [55a], and was recently used in a short enantioselective synthesis of am-... 

Scheme 8.30 Nickel-catalyzed reductive coupling of alkynes with epoxides.

For (hydroxymethyl)allylation via palladium catalyzed reductive coupling of vinyl epoxides, see [305, 306]. 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

Catalytic reductive coupling of epoxides (82, R1 = alkyl) with aldehydes (83) yields /3-hydroxy ethers (84), in a C-0 bond-forming process involving yields up to 90%.311 The reaction is catalysed by (Ph3P)3RuCl, a species which cannot reduce the aldehyde... 

The complex formed on addition of cuprous iodide to a solution of a lithium dialkylamide in ether or tetrahydrofuran is effective in the reductive coupling of allylic halides to give 1,5-dienes with preservation of stereochemistry. This method has been used5 for the stereospecific synthesis of all-trans-squalene and (E,Z,Z,E) squalene from (E,E)- and (Z,JE)-farnesyl bromides, respectively. In an attempted synthesis of (3S)-squalene-2,3-epoxide, 4-[(4R)-2,2,5,5-tetramethyl-l,3-dioxolan-4-yl]butan-2-one (1) and the phosphonium iodide (2) were prepared.6 Unfortu-... 

The deoxygenation of epoxides is not of great preparative value since it involves some loss of stereochemical integrity and the alkenes produced are more readily approached in other ways. Reductive cleavage of ozonides, for example, using triphenylphosphine, commonly forms part of the ozonolysis procedure for conversion of alkenes into carbonyl compounds. If a carbonyl compound is treated with an appropriate P(III) reagent then the reverse process may occur—reductive coupling to form a new C=C double bond. This has found a particularly important... 

Some unsymmetrical tetrasubstituted alkenes (and hence epoxides) have become more available since the advent of McMurry low-valent Ti reductive-coupling procedures and related reactions, but relatively little use has been made of this in epoxide rearrangement studies. An exception involves the cycloheptyl derivative (106 equation 42) which was found to rearrange cleanly to ketone (107). ... 

In the presence of a catalytic amount of SbClj-AgSbFg or PhsC+SbFg, the ringopening rearrangement of epoxides proceeds to generate carbonyl compounds, which subsequently undergo catalytic reductive coupling wifh alkoxysilanes-EtaSiH to yield unsymmetrical ethers (Scheme 14.29) [69]. 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from... 

Raphael, the iodoaromatic (227) is first coupled with the acetylenic alcohol (228) in the presence of Pd° leading to the central intermediate (229). Meyer-Schuster rearrangement of (229) in the presence of methane sulphonic acid then gave rise to (231) presumably via the initially formed ketone (230). Reduction of (231) followed by dehydration next led to (232), which was elaborated to virantmycin, via epoxidation, reduction, deprotection, treatment with thionyl chloride, and finally ester hydrolysis. 

Electrochemical processes can be used for the reduction of many other functional groups. Halogen is removed, as in the reduction of 6-chloro-l-hexene to 1-hexene in 23% yield (in DMF).560 j-y] halides are similarly reduced electrochemically. 2-Chloroaniline, for example, was reduced to aniline in 85% yield. If the electrodes and solvent are changed reductive coupling can occur. 2 Elimination is possible in some cases.Epoxides are opened electrochemically, and hydrogen is often delivered to the more substituted carbon, as in the quantitative conversion of 566 to 567. Azides are reduced to the amine. ... 

The allylic alcohol of 9 was converted to the chloride 10 and coupled with the thioether anion of previously synthesized triene 11 (Scheme 2). The compound 12 now has all 30 carbons, and five double bonds, of squalene epoxide. Reduction with lithium in ethylamine removed the thioether activating group... 

Wilkinson s catalyst can also catalyze the formation of C-0 bonds via a reductive coupling reaction of epoxides with aldehydes in the presence of Et3B as a reductant (eq 77). ... 

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