3-formyl-pinanes

Lazzaroni et al. [67] found that, in the presence of Rh4(CO)j2, isomerization of 1-hexene into preferentially 2-hexene takes place only at higher temperatures. Sterically constrained olefins can easily undergo isomerization into a less congested structure. Dos Santos and Gusevskaya [68] observed in the hydroformylation of a-pinene at 110 C besides 3-formyl-pinane two diastereomers of 10-formyl-pinane (Scheme 5.10). The latter were formed as a result of the rearrangement of the a-isomer to produce the more easily accessible exocyclic... 

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... 

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]. 

When the hydroformylation was conducted with the racemate of a-pinene, the formed aldehydes could be subsequently converted into the corresponding racemic tripinyltrioxanes (Scheme 6.9) [74]. These enantiomers have been separated by two fractional recrystallizations. The trimers were finally cleaved by the effect of acids to give enantiomerically pure 3-formyl-pinanes. 

Scheme 6.9 Production of enantiomerically pure 3-formyl-pinanes via hydroformylation.

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... 

Hydroformylation of (—)- -pinene with hydrogen-carbon monoxide in the presence of cyclo-octa-l,5-dienylrhodium chloride favours the formation of (216 X = CHO), which is readily obtained optically pure via the (-)-tripinyltrioxan with (8-pinene, the preferred product is 10-formyl-c/s-pinane. ° /S-Pinene is converted into the azide (213 X = N3) using Tl(OAc)3-Me3SiN3 cf. Vol. 4, p. 59)." ... 

---