Alkenes, reductive coupling epoxidation

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... 

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). ... 

Scheme 9.7 presents several examples of preparation of alcohols by reduction of epoxides. Coupled with alkene epoxidation, these reduction methods constitute a route for conversion of alkenes to alcohols. 

Solutions of low-valence titanium chloride (titanium dichloride) are prepared in situ by reduction of solutions of titanium trichloride in tetrahydrofuran or 1,2-dimethoxyethane with lithium aluminum hydride [204, 205], with lithium or potassium [206], with magnesium [207, 208] or with a zinc-copper couple [209,210]. Such solutions effect hydrogenolysis of halogens [208], deoxygenation of epoxides [204] and reduction of aldehydes and ketones to alkenes [205,... 

Deoxygenation. This substance reduces epoxides to alkenes in 85-95% yield, generally with retention of configuration, particularly in reduction of trans-tpox-ides. This reduction proceeds more readily than that of carbonyl or ester groups, but a,(3-enals are coupled reductively by 1 at 25° to diallylic ethers. 

Diiodonickel (1 mol%) accelerated significantly many of the reductions performed by Sml2 in THE For example, some epoxides were deoxygenated in good yields to the corresponding alkenes at room temperature in 20 min, 2-octanone gave the pinacol in 10 min (instead of 24 h without catalyst) at room temperature, and cyclohexane carbonyl chloride coupled quantitatively into 2-hydroxy-1,2-dicyclohexylethanone in 1 min (reaction performed in THP). 

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