Bornyl chlorides, reaction

It is best prepared, however, by converting the alcohol, borneol, into bomyl chloride. The bornyl chloride is carefully dried and then gently warmed with an equal weight of aniline. The mixture is then heated to the boiling-point of aniline when the reaction, which is suddenly violent, 18 quickly completed. The reaction mass is neutralised by hydrochloric acid and distilled over in a current of steam. Gamphene is rapidly condensed and solidifies to a crystalline mass. 

Bornene has been prepared from the reaction of 2-bromo-bornane-3-carboxyIic acid with aqueous sodium bicarbonate,6 by pyrolysis of isoborneol methyl xanthate,7 and by the j8-elimination of hydrogen chloride from bornyl chloride with sodium alkoxides in various solvents.2... 

Borneol, camphene, and a-pinene are made in nature from geranyl pyrophosphate. The biosynthesis of a-pinene and the related camphor is described in the chapter. In the laboratory bornyl chloride and camphene can be made from a-pinene by the reactions described below. Give mechanisms for these reactions and say whether you consider them to be biomimetic. 

An efficient route to 7-oxocamphene involved as its key step the solvolytic rearrangement of 3,3-ethylenedioxyisobomyl tosylate (derived from camphor-quinone).621 Brief (3 min 0 °C) treatment (PCl5-CaC03) of borneol gave excellent yields of camphene hydrochloride longer reaction times gave bornyl chlorides.522... 

In our second puzzle, we begin with exactly the same series of reactions from a-pinene hydrochloride (5.46) to camphene (5.50) that we saw in Figure 5.31. They are repeated again in Figure 5.34 to emphasise the difference between the formation of bornyl chloride (5.46) from a-pinene and the formation of isobornyl chloride (5.55) from camphene (5.50). 

The rearrangement in Figure 18.12, giving Mo-bornyl chloride, has been known for over a century. The reaction mechanism can be written in classical terms the right answer is achieved, but should cause us some worries. The migration involves forming a secondary carbocation from a tertiary one, and a single stereoisomer of the product is obtained, for no reason that is readily obvious. There is clearly more to this process than was immediately obvious when it was discovered. 

Reaction of the hydrocarbons in this series with phenols or phenol ethers in the presence of suitable catalysts is well known, a-fenchene and phenol yielding a mixture of o- and p-isofenchylphenols in the presence of aluminium phen-oxide practically the same reaction was described seven years ago. Reaction of camphene with a phenol ester in the presence of stannic chloride is reported to give a bornyl compound, but terpenoid rearrangements are notorious under such conditions, and it is doubtful whether this is the only product. 3,3-Dibromocamphor (261) has been converted into substituted cyclo-hexanecarboxylic acids by the route shown in Scheme 13. ... 

The same products, but in different ratios, occur in the gas phase eliminations of HCl from bornyl and isobornyl chlorides and from the pyrolysis reaction of bornyl and isobornyl benzoates and methyl xanthates . The isobornyl reaction is appreciably faster than that of the bornyl ester ((iso-B/B) = 6.8 at 345 °C), but proceeds at a slightly slower rate than that of cyclohexyl acetate, (CH/iso-B) = 2.1 at 600 °K. By analogy with the nonclassical carbonium ion interpretation of the solvolysis rates of bornyl and isobornyl chlorides, the participation of nonclassical carbonium ion intimate ion-pairs, e.g. 

A specialized cation rearrangement first observed with bornyl systems is the acid catalyzed rearrangement of camphene hydrochloride (73) to isobornyl chloride (76).32 The reaction, which proceeds by a 1,2-alkyl shift called the Wagner-Meerwein rearrangement, initially generates bornyl cation 74, but rearrangement to... 

Amett has determined the heats of formation for 2-norbornyl and 2-methylnor-bornyl ions in a low-temperature calorimeter and a chloride ionization reaction... 

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