0-Pinene transitions

Tackifiers. SBRs have poor tack, so addition of tackifiers is necessary. The tackifier increases the wetting of the adhesive and also increases the glass transition temperature of the adhesive. Typical tackifiers for SBR adhesives are rosins, aromatic hydrocarbon resins, alpha-pinene, coumarone-indene and phenolic resins. 

New chiral oxazaborolidines that have been prepared from both enantiomers of optically active inexpensive a-pinene have also given quite good results in the asymmetric borane reduction of prochiral ketones.92 Borane and aromatic ketone coordinate to this structurally rigid oxazaborolidine (+)- or (—)-94, forming a six-membered cyclic chair-like transition state (Scheme 6-41). Following the mechanism shown in Scheme 6-37, intramolecular hydride transfer occurs to yield the product with high enantioselectivity. With aliphatic ketones, poor ee is normally obtained (see Table 6-9). 

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... 

Picolinate-N-oxido anion (PICO), transition metal peroxides, 1058, 1095 Picolinic acid (pic), transition metal peroxides, 1054, 1058, 1067, 1076 (—)-/3-Pinene, artemisinin synthesis, 288, 289 Plakorin, 191, 247, 1333 Plakortic add, 190, 191 Plakortin, 190, 191... 

Fig. 2.1.6.7 Epoxidation of (-)-ot-pinene over various homogeneous and immobilized transition metal-salen complexes. = homogeneous complex (QH F, 4.6 mmol pivalic aldehyde, 1.85 mmol (-)-ot-pinene, 25 mg catalyst,...

The second example demonstrated immobilization via ship in a bottle , ionic, metal center, and covalent bonding approaches of the metal-salen complexes. Zeolites X and Y were highly dealuminated by a succession of different dealumi-nation methods, generating mesopores completely surrounded by micropores. This method made it possible to form cavities suitable to accommodate bulky metal complexes. The catalytic activity of transition metal complexes entrapped in these new materials (e.g, Mn-S, V-S, Co-S, Co-Sl) was investigated in stereoselective epoxidation of (-)-a-pinene using 02/pivalic aldehyde as the oxidant. The results obtained with the entrapped organometallic complex were comparable with those of the homogeneous complex. 

In the second step, achiral 9-borabicyclo[3.3.1]nonane (9-BBN) adds to the less hindered diastereotopic face of a-pinene to yield the chiral reducing agent Alpine-Borane. Aldehydes are rapidly reduced to alcohols. The reaction with deuterio-Alpine-Borane, which yields (R)-a-d-henzy alcohol in 98% enantiomeric excess ( ) reveals a very high degree of selectivity of the enantiotopic faces of the aldehyde group in a crowded transition state ... 

Chromophores which are asymmetric by nature are characterized by the absence of a center and plane of symmetry in the group of atoms participating in the optical transition. The rotational strength of these are usually larger when compared with chromophores that become optically active due to substitution. This is demonstrated in Mason and Schnepp s8 study of trans-cyclooctene, a-pinene and /1-pi none. They pointed out that the g (anisotropy factor, g = Ae/e) value of the major bands in trans -cyclooctene is relatively high as expected for an intrinsically asymmetric chromophore when compared with the other two olefins. 

Borane ). This reagent is commercially available or prepared by hydroboration of (-)-a-pinene (16) with 9-BBN (17).10 The stereoselectivity of carbonyl group reduction with (S)-Alpine Borane is explained via six-membered transition state 18. 

Ti-Beta was also applied in the selective transformation of a-pinene oxide to camphenolenic aldehyde.78 A selectivity of over 98% was observed in the gas-phase reaction that was explained as a combination of a Lewis catalysed reaction in the absence of Brpnsted acid sites. Furthermore the concentration of a-pinene oxide in the zeolite pores was found to be an important factor not ruling out additional transition state selectivity as well. 

The same authors published a detailed report on the calculations of the oxygen insertion into unactivated C-H bonds by dioxiranes using DFT theory and on comparison of the transition structures for stepwise routes via radical pairs with the concerted pathway <2003JOC811>. The articles dealing with the mechanism of OH formation from ozonolysis of isoprene and a- and /3-pinene provide DFT and ab initio calculation results also for the dioxirane formation <2001CPL(358)171, 2002JA2692, 2005JCP114308>. 

Scott and Wrixon have developed a quadrant rule for the c.d. of platinum(ii)-olefin complexes that depends on d-d orbital transitions. Application of the rule to monoterpenes was considered, and generally conformed to expectations based on known absolute configurations, but in some cases (notably 8-pinene) the results were not satisfactory. The complex measured may be that of a-pinene, for which a Cotton curve of the opposite sign is predicted. Further work on the use... 

T e 1. Glass transition temperature of poly(isobutylene-co-P-pinene)... 

Fig. 1. Glass transition temperature dependence on poly(isobutylene-co-p-Pinene) Composition...

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