McMurry deoxygenative

An intermoleeular McMURRY deoxygenative eoupling of retinal (vitamin A aldehyde) finally yields p-earotene... 

Deoxygenative Coupling of Carbonyl Compounds to Olefins McMurry Coupling... 

Intramolecular McMurry olefmation was realized by Furstner et al., who achieved synthesis of indol derivatives with a catalytic amount of TiCls. They employed zinc metal as a reductant and Me3SiCl as a deoxygenating agent... 

Scheme 4 gives the endgame from Corey s cyclization product 4 (Scheme 1) to the marine natural product scalarenedial (20, [15]), which is a strong fish feeding deterrent. The Barton-McCombie process [16] was employed to deoxygenate at C3, followed by conversion of the ketone to the vinyl triflate 18 with PhNTf2 (McMurry s method [17]). After hydroxy-desilylation of 18, the carbonylation to 19 was catalyzed by Pd(dppp) (see above). The vicinal... 

Titanium promotes the pinacol coupling and then deoxygenates the products the McMurry reaction... 

In 1977, McMurry and Kees [152] developed a titanium-induced intramolecular coupling procedure to form cycloalkenes from dicarbonyl compounds. Mechanistically, as shown in Scheme 85, the coupling reaction proceeds by an initial pinacol dimerization of the dicarbonyl 253 to 254, followed by titanium-induced deoxygenation to afford alkene 255. 

Scheme 4.45 Mechanism of the McMurry reductive deoxygenation of aidehydes and ketones...

The inter- and intramolecular coupling of two carbonyl groups of aldehydes or ketones in the presence of a low-valent titanium species produces a C-C bond with two adjacent stereocenters, a 1,2-diol (a pinacol). These may be further elaborated into ketones by the pinacol rearrangement or be deoxygenated to alkenes (McMurry reaction). 

Another unique method for the synthesis of [6]paracyclophane derivatives was developed by Tochtermann, which was based on the deoxygenation of oxepinophane using the McMurry s reagent (Scheme 5) [13]. The oxepinophane... 

Several other methods for the synthesis of PPVs have been described in the literature. The McMurry reaction, which consists of the deoxygenative coupling of aromatic dialdehydes in the presence of titanium compounds, has been employed to obtain 2,5-dihexyl-PPVs [69], para- and meta-FFV (20) [70], Scheme 11, the latter very unlikely to be prepared by the Wessling-Zinmerman or electrochemical routes, since there is no possibility of forming the required quinodimethane intermediate. Nevertheless, a drawback of this method is the somewhat tedious workup needed for the isolation of insoluble PPVs from the elementary metal powder (Ti and/or Zn), which is also produced. 

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