Pinenes fragmentation

From CD and NMR measurements, these were assigned triple-helical structures in which enantiomerically pure, homochiral configurations occur at the metal centres. In effect, the chirality associated with the pinene fragments appears to direct the assembly process such that only one isomer of the resultant dinuclear... 

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. 

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. 

A more exciting example is the epoxide 56 of natural a-pinene 55 that rearranges to the unsaturated aldehyde 57 in excellent yield.11 Epoxide opening to give the more substituted carbocation is followed by rearrangement 59 and then fragmentation 58. Note that the expansion of the strained four-membered ring is preferred to any alternatives. 

First examples of chiral boratabenzene complexes, which are of interest owing to potential applications as enantioselective catalysts, have recently been reported. The planar chiral chrominm tricarbonyl complex (137) was obtained by addnct formation between borabenzene and an (S)-valinol-derived oxazoline ligand. The Cr(CO)3 fragment stereoselectively complexes with this borabenzene addnct. A different approach has been chosen by Herberich, who developed the chiral boratabenzene ligand (138), which is derived from a-pinene. ... 

The stereochemistry of the addition reactions to the alkene of a-pinene is dominated by the geminal methyl groups of the four-membered ring, which hinder addition from the same face. These methyl groups hinder the approach of a nucleophile to the rear of the epoxide. The fragmentation to form sobrerol also involves the release of the strain of the cyclobutane ring. 

The radical reaction of carbon tetrachloride with aliphatic double bonds involves addition of the trichloromethyl radical to the double bond, followed by chlorine atom abstraction from carbon tetrachloride by the intermediate radical to give the product. After the addition of the trichloromethyl radical to /3-pinene, a fragmentation occurs prior to formation of the product. 

The radical addition of thiolacetic acid to )3-pinene gives unrearranged product. This result is evidence for the discrete existence of radical 5-9. That is, the rate of abstraction of a hydrogen atom from thiolacetic acid by 5-11 is faster than its rate of fragmentation. Note that the product is a mixture of stereoisomers, as indicated by the wavy bond lines. 

A cyclopentane aldehyde (297) is obtained when verbenone epoxide (298) is treated with zinc bromide. The presence of pinene in the products is difficult to explain, and the difference in products obtained with aluminium chloride (Vol. 1, p. 45) is remarkable. When the toluene-p-sulphonylhydrazone of the epoxide (298) is treated with potassium t-butoxide, both isomers of the cyclobutyl-acetylene (299) are obtained in an Eschenmoser fragmentation. ... 

In a synthesis which correlates (-)-3-pinene with (+)-hinesol (41 Scheme 15), Magnus started with (+)-nopinone (37) which provided, after several steps, the sulfone (38) as the key compound. Under airline conditions, (38) gives the p-keto sulfone (40) via intramolecular attack of the carbanion of (38) forming the alkoxide (39). Release of ring strain is responsible for the domination of the ft gmentation rather than typical alternatives such as oxetane formation, substitution, or other reaction pathways. Traces of water in the fragmentation step give rise to the formation of carboxylic acid (42). 

The free radical polymerization of pinenes and limonene is of little interest, because of the modest yields and DPs obtained with their homopolymerizations. However, their copolymerization with a variety of conventional monomers has been shown to produce some interesting materials, particularly in the case of controlled reversible addition fragmentation chain-transfer (RAFT) systems involving P-pinene and acrylic comonomers [5]. 

Further details of phase-transfer addition of dibromocarbene to a,(3-unsaturated esters and ketones [e.g. (18)] and subsequent reductive monode-bromination with tributyltin hydride (Vol. 7, p. 34) have been publishedJulia reports the use of solid NaOH-Et3NCH2Ph CP for the solid-liquid phase-transfer catalytic generation of dichlorocarbene (addition to a-pinene and limonene). Dichlorocarbene also provides a mild and efficient method for the Beckmann fragmentation of anh-a-hydroxy-ketoximes into aldehydes (or ketones) and nitriles [e.g. 2-exo-hydroxy-3-hydroxyiminobornane into (24 X = CHO, Y = CN)]. Trimethylsilylcyclopropanes are synthesized by adding the... 

Either direction of cleavage of the primary ozonide from a-pinene would produce a carbonyl oxide with ten carbon atoms. Fragmentation of this intermediate might well lead to a number of hydroperoxides we could detect, but only MHP was observed from gas-phase ozonolysis. As in the case of isoprene, neutralisation of the sample from aqueous ozonolysis before analysis indicates that significant amounts of HAHPs are formed in water. These are still under investigation. 

There have been reports in which j3-pinene was copolymerized by a radical copolymerization, reversible addition-fragmentation chain transfer (RAFT). As comonomers, methyl acrylate or n-butyl acrylate have been used (9,10). 

Wang Y., Li A.L., Liang LL., Lu J., Reversible addition-fragmentation chain transfer radical copolymerization of beta-pinene and methyl acrylate, Eur. Polym. J., 42(10), 2006, 2695-2702. 

The synthesis of (+ )-sesquifenchene (450) and of ( )-epi-P-santalene (451) from the common intermediate (449), derived from endo-dicyclopentadiene, has been detailed. Conversion of (449) into the precursor of (450) makes use of the skeletal rearrangement that occurs during solvolysis of active 2-norbornyl esters. In a synthesis of (-H )-hinesol (452) and 10-epi-(-l-)-hinesol, interesting use has been made of a fragmentation reaction.The tosyl derivative (453), which was obtained in several steps from ( —)-P-pinene, was converted into the spiro[4,5]decane (455) on treatment with sodium hydride in DMSO the essential stereoelectronic changes are summarized in the intermediate (454). 

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