Decarbonylation, of aldehydes

The chiral aldehyde 88 was decarbonylated to give 89 with overall retention of the stereochemistry [45]. The unsaturated aldehyde in the polyfunctionalized molecule 90 was decarbonylated smoothly to afford alkene 91 [46]. The decarbonylation of aldehydes catalysed by a supported Pd or Rh complex is carried out at high 

Although the decarbonylation of aliphatic acyl halides is possible with the Rh complex, a mixture of alkenes is obtained [43,44], 

---

In certain sensitive compounds, such as triphenylacetyl chloride, decar-bonylation may be the major reaction (59). Palladium, the preferred catalyst for the Rosenmund reduction, is also an excellent catalyst for decarbonylation of aldehydes (27,28,65), and decarbonylation may occur after aldehyde formation. 

Decarbonylation of Aldehydes Using Ruthenium(II) Porphyrin Catalysts... 

We recently reported briefly on an extremely efficient thermal catalytic decarbonylation of aldehydes using a system based on Ru(TPP)(PPI13)2 (6), and report here further studies on this system and one based on Ru(TPP)(CO)(tBu2P0H). 

Table. Decarbonylation of aldehydes using a Ru(TPP) (PPh /HBu P catalyst system...

Methyl deoxypodocarpate 127 (Scheme 1) 129) represents a simple problem since the ketone 132 is well-known and readily available from Hagemann s ester in three steps. The problem of geminal alkylation of this ketone stems from its existence as an EjZ mixture of ring fusion isomers. Recognizing that decarbonylation of aldehydes occurs readily with Wilkinson s catalyst creates a structural equivalence of an acetaldehyde chain and a methyl group as in 128. This simple relationship immediately establishes several options, a simple one uses a thioacetal such as 129 as a synthon for the aldehyde. The presence of a carbonyl group three carbons away... 

The facile formation of metal carbonyl complexes makes rhodium a very useful catalyst for both the hydroformylation of multiple bonds and the decarbonylation of the aldehydes. Two groups have independently utilized the metal carbonyl complex obtained from decarbonylation of aldehydes in the PK reaction (Scheme 11.11) [24]. 

Alaimo, P.J.. Arndtsen, B.A. and Bergman. R.G. (2000) Alkylation of iridium via tandem carbon-hydrogen bond activation/decarbonylation of aldehydes. Access to complexes with tertiary and highly hindered metal-carbon bonds. OrganometaUics, 19 (11), 2130-2143. 

Decarbonylation of Aldehydes and Acyl Halides Carbonyl-extrusion... 

CO into a metal-hydrogen bond, apparently analogous to the common insertion of CO into a metal-alkyl bond (6). Step (c) is the reductive elimination of an acyl group and a hydride, observed in catalytic decarbonylation of aldehydes (7,8). Steps (d-f) correspond to catalytic hydrogenation of an organic carbonyl compound to an alcohol that can be achieved by several mononuclear complexes (9JO). Schemes similar to this one have been proposed for the mechanism of CO reduction by heterogeneous catalysts, the latter considered to consist of effectively separate, one-metal atom centers (11,12). As noted earlier, however, this may not be a reasonable model. 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Catalytic decarbonylation of aldehydes has been studied using mono- and bisdiphosphine complexes of Rh(I). The catalyst [Rh(dppp)2]BF4f where dppp = 1,3-bis( diphenylphosphino)propane, decarbonylates al-... 

Decarbonylation of aldehydes and acid halides is an important synthetic reaction (i, 2) and using various transition-metal complexes as stoichiometric or catalytic reagents for this process has... 

Equations 2c and 2d show the acyl-alkyl migration and reductive elimination steps, respectively. There is good evidence that this same mechanistic scheme applies to the decarbonylation of aldehydes (see Equation set 2, X = H), although in this case reaction intermediates have not been isolated (3, 5, 9, 18). Additionally, evidence exists that the rate-determining step is oxidative addition for aldehyde decarbonylation (see Equation 2b, X = H) (3, 9, 18). Several recent reports have shown that for some special aldehydes, oxidative addition of the carbonyl-hydrogen bond indeed does occur using rhodium(I) complexes (8,19). In these studies a stable chelate was formed after oxidative addition that enabled isolation and characterization of the products (8, 19). 

CO formed through the decarbonylation of aldehydes may poison noble metal catalysts,... 

---