CATALYTIC HYDROFORMYLATION OF (1S,5S)-(-)-BETA-PINENE AND (1R,5R)-(-BETA-PINENE - STEREOSELECTIVE SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF (1S,2R,5S)-, (1S,2S,5S)-10-FORMYLPINANE, (1R,2R,5R)-10-FORMYLPINANE AND (1R,2S,5R)-10-FORMYLPINANE())
F. Azzaroni et al., CATALYTIC HYDROFORMYLATION OF (1S,5S)-(-)-BETA-PINENE AND (1R,5R)-(-BETA-PINENE - STEREOSELECTIVE SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF (1S,2R,5S)-, (1S,2S,5S)-10-FORMYLPINANE, (1R,2R,5R)-10-FORMYLPINANE AND (1R,2S,5R)-10-FORMYLPINANE()), Journal of organometallic chemistry, 508(1-2), 1996, pp. 59-67
(1S,5S)-(-)- and (1R,5R)-(+)-beta-pinene have been hydroformylated in
toluene to give (1S,2R,5S)- and (1R,2S,5R)-10-formylpinane with up to
95% diastereoselectivity using bimetallic CoRh(CO)(7) as a catalyst; t
he latter was generated in situ from preformed Co2Rh2(CO)(12) or a sto
ichiometric mixture of either [Rh-4(CO)(12)] or [Rh-6(CO)(16)] and [Co
-2(CO)(8)]. At 70-125 degrees C and under 60 arm of syngas, the yields
of hydroformylated products do not exceed 30% because of the concomit
ant isomerization of beta- to alpha-pinene. In all cases the catalyst
is recovered as a mixture of soluble cobalt carbonyl derivatives and a
crystalline precipitate that contains most of the rhodium, mainly as
[Rh-6(CO)(16)]. Comparable yields and diastereoselectivities were obta
ined from reactions in tetrahydrofuran with a mixture of [Rh-4(CO)(12)
] and [N(PPh(3))(2)]Cl as the catalyst precursor. The corresponding (1
S,2S,5S)- and (1R,2R,5R)-10-formylpinanes, along with the correspondin
g alcohols, were obtained diastereoselectively by use of bimetallic Co
-Rh or homometallic Rh carbonyl catalysts modified with bis(diphenylph
osphine)ethane (dppe). When unidentate phosphines such as triphenylpho
sphine were used in place of dppe, as the ligand/metal (L/M) ratio was
raised the diastereoselectivity of both the hetero- and the homo-meta
llic catalytic system fell progressively, and was completely lost for
L/M greater than or equal to 4. However, a further increase in L/M to
ca. 70-100 allows chemio- and diastereo-selective synthesis of both th
e (1S,2S,5S)- and (1R,2R,5R)-10-formylpinane. The (1S,2R,5S)-, (1S,2S,
5S)-, (1R,2R,5R)- and (1R,2S,5R)-10-formylpinane diastereomers were is
olated by distillation under reduced pressure and fully characterized
by IR, UV, H-1 and C-13 NMR and circular dicroism (CD) spectroscopy, a
nd mass spectrometry. The possible factors favouring the diastereosele
ctive hydroformylation of beta-pinenes under the conditions used are d
iscussed.