Alkenes reductive coupling with carbonyl compounds

Organotitanium and -zirconium chemistry already has an established place in organic synthesis and many reactions are covered elsewhere in the Practical Approach series. Examples include reductive coupling of carbonyl compounds with low valent titanium to form 1,2-diols or alkenes methylenation of ester carbonyl groups with titanocene methylidene (Cp2Ti=CH2) zirconium-catalysed methylalumination of alkynes and hydrozirconation of alkynes and alkenes with the Schwartz reagent, Cp2ZrHCl. ... 

Reductive coupling of polyhaloalkanes with carbonyl compounds in the presence of Zn is used in the synthesis of various halogen-substituted alkenes. For example, the reaction of benzaldehyde with the organozinc reagent 4.101 gives the trifluoromethyl-substituted alkene 4.102 (Scheme 4.50). 

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... 

A wide range of alkenic compounds exhibiting interesting properties associated with their ir-systems have been elaborated via the reductive coupling carbonyls. For example, Marshall and coworkers have studied the intramolecular McMurry reaction as a route to betweenanenes, a class of conformationally... 

In its original form,94 the Julia reaction consisted of the formation of a carbon-carbon double bond through the coupling of a sulfonyl-stabilized anion and a carbonyl compound to generate a P-hydroxy sulfone, followed by a reductive elimination to afford the alkene (Eq. 47). A subsequent study of its scope and stereochemistry led to improved reaction conditions, which are now widely used.206 Alternative methods to synthesize the P-hydroxy sulfone intermediates, such as the addition of sulfonyl carbanions to esters with subsequent reduction of the ketone to the P-hydroxy sulfone, are also known (Eq. 121).207... 

Carbon-heteroatom double bonds can also participate in this reaction. These include both carbonyl compounds (Scheme 11.37) and imines (Scheme 11.38). Addition to aldehydes is co-catalysed by tin(II) or indium(III) salts. Under these conditions, tetrahydrofiirans are obtained. The presence or absence of the co-catalyst can also switch the reaction from one mode to another (Scheme 11.39). An indium cocatalysed cycloaddition to a 7-pyrone aldehyde 11.117 was used in a synthesis of aureothin 11.122 and A-acetylaureothamine 11.123 (Scheme 11.40). Cross-metathesis of the exo-cyc ic alkene 11.118 allowed a subsequent Suzuki coupling with a gem-dibromide 11.120 that showed the expected selectivity (Section 2.1.4.2). This reaction required the use of thallium ethoxide as the Lewis base to suppress the formation of side products. A Negishi coupling completed the synthesis of aureothin 11.122. Reduction and acylation of the nitro group yielded A-acetylaureothamine 11.123. The latter compound is active digainst Helicobacter pylori, a bacterium behind stomach ulcers. 

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