3-Pinene synthesis

Among chiral dialkylboranes, diisopinocampheylborane (8) is the most important and best-studied asymmetric hydroborating agent. It is obtained in both enantiomeric forms from naturally occurring a-pinene. Several procedures for its synthesis have been developed (151—153). The most convenient one, providing product of essentially 100% ee, involves the hydroboration of a-pinene with borane—dimethyl sulfide in tetrahydrofuran (154). Other chiral dialkylboranes derived from terpenes, eg, 2- and 3-carene (155), limonene (156), and longifolene (157,158), can also be prepared by controlled hydroboration. A more tedious approach to chiral dialkylboranes is based on the resolution of racemates. /n j -2,5-Dimethylborolane, which shows excellent enantioselectivity in the hydroboration of all principal classes of prochiral alkenes except 1,1-disubstituted terminal double bonds, has been... 

The production of myrcene (7) from P-pinene is important commercially for the synthesis of a wide variety of flavor and fragrance materials. Some of those include nerol and geraniol, citroneUol (27) and citral (5). 

One method of synthesis of taxol analogues starts with a-pinene (8), the readily available and inexpensive monoterpene derived from the processing of turpentine from the pine tree (200). The a-pinene is oxidized to verbenone, which is then alkylated and converted to taxol analogues in a multistep process. 

The synthesis and purification of cumyl alcohol (CumOH), p-dicumyl methyl ether (DCE)) and 2-chloro-2,4,4-trimethylpentane (TMPC1), and the sources and purification of methyl chloride (MeCl), methylcyclohexane (MCHx), isobutylene have been described [9, 10]. P-Pinene (P-PIN), (Aldrich), was chromatographed over alumina (activity I, Fisher), and freshly distilled over CaH2 under nitrogen according to 1H-NMR spectroscopy and GC analysis the purity was >99%. 2,6-Di-/er/-butylpyridine (DtBP), (Aldrich), anhydrous A,A-dimethylacetamid (DMA), (Aldrich), ethylaluminum dichloride (EtAlCl2), 1.0 M solution in hexanes (Aldrich), and methanol (Fisher) were used as received. 

Synthesis of High Molecular Weight Poly (p-Pinene)... 

Liu H. J., Chew S. Y., Yeh W. L. Facile Selective Diels-Alder Reactions of Chiral 5,5-Dimethyl-4,6-Methano-2-Methoxycarbonyl-2-Cyclohexenone. Application to the Total Synthesis of Qinghaosu. Youji Huaxue 1993 13 314 321 Keywords (-)-/f-pinene, asymmetric synthesis... 

The activity of the FePeCli6-S/tert-butyl hydroperoxide (TBHP) catalytic system was studied under mild reaction conditions for the synthesis of three a,p-unsaturated ketones 2-cyclohexen-l-one, carvone and veibenone by allylic oxidation of cyclohexene, hmonene, and a-pinene, respectively. Substrate conversions were higher than 80% and ketone yields decreased in the following order cyclohexen-1-one (47%), verbenone (22%), and carvone (12%). The large amount of oxidized sites of monoterpenes, especially limonene, may be the reason for the lower ketone yield obtained with this substrate. Additional tests snggested that molecular oxygen can act as co-oxidant and alcohol oxidation is an intermediate step in ketone formation. 

The synthesis of the Taxol in Scheme 13.56 by P. A. Wender and co-workers at Stanford University began with an oxidation product of the readily available terpene pinene. One of the key early steps was the photochemical rearrangement in Step B. 

In Holton s and Wender s work, the total synthesis was achieved by sequentially forming the AB ring through the fragmentation of epoxy alcohols derived from (—)-camphor and a-pinene. Nicolau s, Danishefsky s, and Kuwa-jima s total syntheses involved B ring closure connecting the A and C rings, whereas in Mukaiyama s synthesis, the aldol reaction was extensively applied to construct the polycyclic system. 

Metal complexes of pinene-fused boratabenzene ligands, analogous to chiral metallocenes that have found application in catalysis and enantioselective synthesis, have been prepared.122-124 With late transition metals such as Mn and Fe, the complexes are obtained as mixtures of diastereomers (e.g., 97) with the sterically less congested exo form predominating, but the bis(ligand) Zr complex 98 was obtained as the pure exo,exo product.124 A lithium... 

Terpenes Terpenes [a-pinene (1), /f-pinene (2), and limonene (3)] are employed in the synthesis of flavors and fragrances (F F), although these compounds are often obtained by catalytic routes from hydrocarbons. 

Linalool is an important fragrance and fragrance precursor (esters) with an annual production of over 15 000 t. Some 50% is made by semi-synthesis from a- and / -pinene, the other part is made synthetically starting from isobutene via 6-methylhept-5-en-2-one (9). Addition of an acetylene fragment followed by partial hydrogenation (Pd) leads to linalool. 

Another opportunity to combine two reaction steps towards a one pot synthesis is the epoxidation of a-pinene and the isomerization of the epoxide to campho-lenic aldehyde (Scheme 5.6). Zeolite Ti-Beta seems adequate to deal with both steps as a catalyst [24]. Campholenic aldehyde is the starting material for several sandalwood fragrances. 

Ripperton, L. A., and D. Lillian. The effect of water vapor on ozone synthesis in the photo-oxidation of alpha-pinene. J. Air Pollut. Control Assoc. 21 629-635, 1971. 

Carbocation rearrangements synthesis of camphor from a-pinene... 

---