McMurry reagent reductive preparation

Cycloalkenes. McMurry and Kees have described an intramolecular coupling of dicarbonyl compounds to cycloalkenes. In the intermolecular version of this reaction titanium(O) powder obtained by reduction with potassium or lithium is used (7, 368). In the intramolecular reaction a superior coupling reagent is prepared by reduction of TiClg with a zinc/copper couple in DME. 

Alkenes can be obtained from aldehydes or ketones on reductive dimerization by treatment with a reagent prepared from titanium(III) chloride and zinc-copper couple (or L1A1H4), or with a species of active titanium metal formed by reduction of titanium(III) chloride with potassium or lithium metal. This McMurry coupling reaction is of wide application, but in intermolecular reactions generally affords a mixture of the E- and Z-alkenes (2.99). 

Reductive coupling of carbonyl compounds to olefins. Reductive coupling of carbonyls to olefins with a low-valent titanium reagent prepared from TiCla and LiAlHi (6, 589) tends to give erratic yields. McMurry and Fleming find that use of Ti(0) gives reproducible results. Yields are somewhat higher with metal prepared with potassium, but lithium is easier to handle. 1,2-Diols are also reduced to olefins. ... 

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