Nopol

Uses ndReactions. Some of the principal uses for P-pinene are for manufacturing terpene resins and for thermal isomerization (pyrolysis) to myrcene. The resins are made by Lewis acid (usuaUy AlCl ) polymerization of P-pinene, either as a homopolymer or as a copolymer with other terpenes such as limonene. P-Pinene polymerizes much easier than a-pinene and the resins are usehil in pressure-sensitive adhesives, hot-melt adhesives and coatings, and elastomeric sealants. One of the first syntheses of a new fragrance chemical from turpentine sources used formaldehyde with P-pinene in a Prins reaction to produce the alcohol, Nopol (26) (59). 

The acetate is also usehil commercially and can be made by direct esterification of Nopol. The products are usehil in soaps, detergents, poHshes, and other household products. 

No observed effect level (NOEL), 18 548 of aquatic toxicity, 25 887 Noodle washing, 19 184-185 Nootkatone, 24 549 Nopol, 24 497... 

Addition of alane and borane to alkenes affords a host of alkylated alanes and boranes with various reducing properties (and sometimes bizarre names) diisobutylalane (Dibal-H ) [104], 9-borabicyclo[3.3.1]nonane (9-BBN) (prepared from borane and 1,5-cyclooctadiene) [705], mono- [106,107] and diiso-pinocampheylborane (B-di-3-pinanylborane) (both prepared from borane and optically active a-pinene) [108], isopinocampheyl-9-borabicyclo[3.3.1 Jnonane alias B-3-pinanyl-9-borabicyclo[3.3.1]nonane (3-pinanyl-9-BBN) (prepared from 9-borabicyclo [3.3.1]nonane and a-pinene) [709], NB-Enanthrane prepared from 9-borabicyclo[3.3.1]nonane and nopol benzyl ether) [770] and others. ... 

Reduction of a, -acetylenic ketones with chiral borane NB-Enanthrane prepared by addition of 9-borabicyclo[3.3.1]nonane to the benzyl ether of nopol yielded optically active acetylenic alcohols in 74-84% yields and 91-96% enantiomeric excess [770]. Another way to optically active acetylenic alcohols is reduction with a reagent prepared from lithium aluminum hydride and (2S, 3R)-( -I- )-4-dimethylamino-3-methy 1-1,2-dipheny 1-2-butanol. At —78° mainly R alcohols were obtained in 62-99% yield and 34-90% enantiomeric excesses [893]. 

The (IR)-nopadiene is prepared from commercially available (Aldrich Chemical Company, Inc.) (lR)-(-)-nopol (Note 3) according to the following... 

Pinene is similar to a-pinene in its reactions. Pyrolytic cleavage to myrcene, the starting material for acyclic terpenes, is used on an industrial scale. Addition of formaldehyde results in the formation of nopol nopyl acetate is used as a fragrance material. /3-Pinene is produced in large quantities by distillation of turpentine oils. It is used as a fragrance material in household perfumery. However, most /3-pinene is used in the production of myrcene. 

Dihydroxylation of hindered double bonds. The a-pinene derivative 1 (Nopol) is hydroxylated in low yield by osmium tctroxide and f-butyl hydroperoxide. Hydroxylation is effecled in 62% yield by use of 0s04 in combination with trimethylamine N-oxide as oxidant and pyridine as base. This method is generally suitable for hindered alkenes (yields 78-93%). 

NB-Enantrane (1). This is the trademark of Aldrich for the 9-BBN adduct of the benzyl ether of 6,6-dimethylbicyclo [3.1.1] hept-2-ene-2-ethanol (nopol). 

Figure 15. Backscattering DCPi ROA and Raman spectra for lR-(-)-nopol.

Nopol, 2-cyclohexylethanol, and decanol have been converted to the corresponding acetylenic ethers in 64, 68, and 71% yield, respectively. Although 1-adamantanol can be transformed to adamantyloxyacetylene in 92% yield, other acetylenic ethers derived from tertiary alcohols have been found to be unstable to purification (unpublished results). See Peric s, M. A. Serratosa, F. Valenti, E. Tetrahedron 1987, 43, 2311-2316. 

The nopol derivative (5) has advantages in some cases but the most striking advance has been the introduction of commercially available chloroborane (6). Compound (6) is a stronger Lewis acid than (4) or (5) and also less subject to steric hindrance. It readily reduces acetophenone (98% ee),... 

Preparative Methods NB-Enantrane may be prepared by hydroboration of nopol benzyl ether (commercially available, or from nopol and benzyl bromide ) with 9-Borabicyclo[3.3.1]nonane (9-BBN) (eq 1). 

Asymmetric Reductions. NB-Enantrane is an analog of B-3-Pinanyl-9-borabicyclo[3.3.1 Jnonane (Alpine-Borane ). Since the absolute configuration of nopol is the opposite of (+)-a-pinene, the reagent provides the opposite mode of asymmetric induction. The reagent provides higher asymmetric induction than Alpine-Borane for cases where the two groups flanking the ketone are relatively small, such as methyl or ethyl alkynyl ketones (eq 2). 

The reagent presumably leads to higher asymmetric induction because of the increased size of the nopol side chain. Brown has shown that replacing the vinylic methyl group of a-pinene with larger groups also leads to higher asymmetric induction (eq 3). ... 

Synthetic applications of this methodology have been made and mechanistic investigations have been carried out. Reagents (133) and (134), derived, respectively, from addition of 9-borobicy-clo[3.3.1]nonane to p-pinene and nopol benzyl ether, are also capable of delivering a single hydride equivalent with good enantioselectivity. ... 

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