Rearrangement of camphor

Recently, Gartner and colleagues have reported the [1,2]-Wittig rearrangement of camphor-derived acetal 39 to 40 (equation 21) . 

Langlois and co-workers ° developed a stereoselective hetero-Claisen rearrangement of camphor-based oxazoline A -oxides 300, available from hydroxylami-noisobomeol 298 and orthoesters 299. The rearrangement, initiated by acylation of... 

For an excellent formal treatment of the Wagner-Meenvein rearrangements of camphor in sulfuric acid, which makes extensive use of C labeling, see O. R. Rodig and R. J. Sysko, J. Am. Chem. Soc., 94, 6475 (1972). 

There are regularly publications concerning the transformation of bomane derivatives [particularly camphor (40) oxime] to campholenyl derivatives, but there is no particular interest attached to them as syntheses of natural products. Nevertheless, we mention work on the Beckmann-type rearrangements of camphor oxime,and a route to campholenic alcohol (352) from the hydroxycamphene 353. "Y-Campholenol (354) has been identified in Tanacetum... 

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

Another enantiospecific synthesis of longifolene was done starting with camphor, a natural product available in enantiomerically pure form (Scheme 13.26). The tricyclic ring system is formed in step C by an intramolecular Mukaiyama reaction. The dimethyl substituents are formed in the first step of sequence E by hydrogenolysis of the cyclopropane ring. The final step of the synthesis involves a rearrangement of the tricyclic ring system that is induced by solvolysis of the mesylate intermediate. 

Beckmann rearrangement of 6-endo-chlorocamphor oxime (Vol. 7, p. 43) yields (220) and the cis- and frans-ring-fused (221), and camphor oxime rearranges with hydrazoic acid in polyphosphoric acid to yield (222). ... 

Exercise 30-7 Camphor can be made on an industrial scale from a-pinene (turpentine) by the following reactions, some of which involve carbocation rearrangements of a type particularly prevalent in the bicyclic terpenes and the scourge of the earlier workers in the field trying to determine terpene structures. 

The 3 + 2-cycloaddition of commercially available Me3SiCHN2 with camphor sultam-derived dipolarophiles produces 3-trimethylsilyl-substitutcd-A1 -pyrazolincs which on acid treatment convert into optically active A2-pyrazolines.60 The nucleophilic addition of ethyl diazoacetate with /V-cthoxycarbonyl-/V-(2,2,2-trichlorocthylidcne)a-mine produces a new diazo intermediate (35), which by 1,3-dipolar cycloaddition followed by a sigmatropic rearrangement of the cycloadduct (36) furnishes a substituted pyrazole (37) (Scheme 13).61. 

Camphor is of considerable importance technically, being used in the manufacture of celluloid and medicinal products. It is manufactured industrially from a-pinene, obtained from turpentine, by several processes (66-107) which differ mainly in detail. Synthetic camphor is usually obtained as the racemic modification. The formation of camphor involves the Wagner-Meerwein rearrangements, e.g. ... 

The rearrangements of carbocations also play a role in the formation of ter-pene natural products. Menthol and camphor are examples of terpenes derived from plant oils. They are constructed using a common building block, as shown in Section 25-8, and undergo a series of rearrangements in the course of construction to generate the most stable carbocation. 

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