Cyclic Monoolefins as Substrates

In a few cases, even the raw oils directly isolated from the plant have been submitted to the transformation with syngas [67]. Product aldehydes possess an antimicrobial activity and have a pleasant smell. Therefore they can be used well with malodorous substances. In most cases, Rh or Co catalysts were submitted to hydroformylation. Also Pt/Sn catalysts should be taken into consideration, since undesired Wagner-Meerwein isomerization is suppressed. All aldehydes and acetals, as well as their mixtures, show woody, floral, and green, or balsam-like odors and can be employed as components of perfume accords. 

In contrast, when (—)-a-pinene was reacted in the presence of an unmodified Rh catalyst, mainly (-l-)-3-formyl-pinane was obtained [69-71]. In addition, two diastereomers of 10-formyl-pinane were formed as a result of the isomerization of a-pinene to the more reactive fl-pinene. When the catalyst was modified with P(O-0-fBuPh)3 as Ugand, the reaction could be run under much milder conditions (80 bar, 100 C) [72]. 3-Formyl-pinane was obtained as a main aldehyde with almost 100% stereoselectivity for the trans isomer and a mixture of trans- and cis-lO-formylpinanes (about 1 1). When the reaction was conducted in ethanol 

3-Formyl-pinane can be isolated from the aldehyde mixture as pure compound in moderate yield by distillation with a column of 20 trays [70a]. In turn, the aldehyde was converted into the primary amine by reductive amination with ammonia. The chiral amine has been utilized, for example, for the optical resolution of racemic pantolactone. Alternatively, aldol condensation of the formed aldehydes with ketones and subsequent hydrogenation give alcohols that might have a broad scope of potential applications in perfumes, soaps, and shampoos [73]. 

The corresponding alcohol was formed with only 5% yield. The undesired isomerization into a-pinene, which is noted with Co or mixed Rh/Co catalysts [76], is rather slow. Only 1-5% of this exocyclic olefin has been observed even when a large excess of SnCl2 was used. A phosphine-modified Rh catalyst has been employed at 200 bar to convert P-pinene in 10-formyl-pinane in a 272 g scale to give the product in 67% yield [77, 78]. The reaction can also be run under 

In a similar manner, a modified Rh(PPh3) catalyst was able to convert camphene under neat conditions at 200 bar into the aldehydes [77, 78]. This protocol was carried out in a 400 g scale. When the syngas pressure and temperature were lowered (90 bar, 100 °C), the linear aldehydes were formed in nearly quantitative yields [7 6]. In the presence of phosphorus ligands, the formation of the endo isomer was favored (exo/endo 1 1.5), whereas in immodified systems both exo and endo compounds were formed in nearly equal amounts. Neither steric nor electronic parameters of the Ugands were found to influence significantly the diastereose-lectivity of the rhodium-catalyzed hydroformylation. The reaction was likewise performed in a toluene/water biphasic system employing TPPTS to immobilize the rhodium catalyst in the aqueous phase [84]. A mixture of exo and endo isomers of the linear aldehyde (exo/endo 1/1.5) was obtained in nearly 100% chemoselectivity and 71% yield [Rh(COD)(OAc)]2, TPPTS, CO/Hj (1 1, 8 MPa), 80 C, toluene/water (2.5 1 v/v), 48 h.  

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