5-Methylbicyclo -2-octene

Bicyclo[2.2.2]-2-octene Bicyclo[3.2.1]-2-octene 2-Methylenebicyclo[2.2.1 ]heptane 2-Methylbicyclo[2.2.1 ]-S-heptene ... 

Methylenebicyclo[2.2.2 ]octane 5-Methylbicyclo[2.2.2]-2-octene 2-MethyIene-3-methylbioyclo[2.2.1]heptane 2-Methylene-1-me thylbicyolo[2.2. l]heptane 3 -Methylene-1 - methylbio yolo[2.2.1 ]heptane 2-Methyl-cis-bicyelo[3.3.0]octane (CsHie) 2-Methyl-ci -bicyelo[3.3.0]-2-ootene... 

In this series we may find, besides the methylated homologs of the C8Hi2 hydrocarbons already described, some new products of cycle expansion. The vapor-phase silicophosphoric acid-catalyzed reaction of 2-methylenebicyclo[2.2.2]octane (18) at 195° produces the double-bond isomer (1 ) and a mixture of 1-methyl-, 2-methyl-, and 3-methylbicyclo-3.2.1[octenes] (21, 22, and 23) (Fig. 5) through seemingly parallel reactions (Fig. 6) 15, 16). 

A qualitatively similar mixture is obtained from the 5-methylbicyclo-[2.2.2]-2-octene (20) at 195°. 

However, at 250°, the hydrocarbons 18 or 20 are converted to 2-methyl- and 3-methylbicyclo[3.3.0]-2-octenes (24 and 25) and to the bicyclo[4.3.0]-l-nonene (20) (Fig. 7) 16). The reactions indicated by vertical arrows in Fig. 5 are faster than the horizontal ones, and the hydrocarbons in the same column form quasi-equilibrium mixtures. 

It is interesting to point out that acetolysis of 2-hydroxymethyl-2-methylbicyclo[2.2.1]heptane gives a mixture of methylbicyclo[3.2.1]-octenes including 82% of 36 (26). 

At low conversion, tricyclene is the main product (17% of the monomer containing 50% camphene) (38) then a-terpinene goes through a sharp maximum (39) (Pig. 13), and disappears when camphene vanishes. At this point, 30% of the mixture is spectroscopically identical with the isomers in the products of the limonene reaction (Fig. 1). One of the main components of the final product has been identified as the 2.3-dimethylbicyclo[3.3.0]-2-octene (40), the other being a mixture of two methylbicyclo[4.3.0]octenes (41), easily hydrogenated to 4- and 5-methylperhydrindanes. 

The passage from bicyclo[2.2.2]octane structures to the isomeric bicyclo[3.2.1]octanes is irreversible for all practical purposes in the CsHiz and C9H14 series (it was not investigated in the CioHie series) and this conclusion is substantiated by other facts the acid-catalyzed dehydration of 2-methylbicyclo[3.2.1]-2-octanols and 3-methylbicyclo-[3.2.1]-3-octanols gives small quantities of methylbicyclo[2.2.2]octenes 30), while the acid-catalyzed hydration of bicyclo[2.2.2]-2-octene forms the bicyclo[3.2.1]-2-octanol 27) the nitrous acid deamination of 2-aminobicyclo[2.2.2]-5-octene goes to bicyclo[3.2.1]octenols 31) and the solvolysis of bicyclo[2.2.2]-5-octen-2-ol esters to bicyclo[3.2.1]octenols 32). 

Reactive Intermediates.—Additions of dichlorocarbene to cyclo-octatetraene, bicyclo-[6,l,0]nona-2,4,6-triene, iV-ethoxycarbonylazepine, cycloheptatriene, and related compounds have been studied, and the stereochemistry of the products explained in terms of approach of the carbene from the least hindered direction, e.g. cyclo-octatetraene gave only one bis-adduct (172). Treatment of cyclo-octene with 1,1-dichloroethane and n-butyl-lithium gave 9-chloro-9-methylbicyclo[6,l,0]nonane, which was converted into 9-methylenebicyclo[6,l,0]nonane using potassium t-butoxide this procedure has been developed into a general preparation of methylene-cyclopropanes. ... 

The 2-hydroxyhomotropylium ion has been generated by protonation of bicyclo-[5,l,0]octa-3,5-dien-2-one and isomerized by irradiation at — 70°C to its 1-hydroxy-isomer, which gives cyclo-octa-2,4,6-trienone on deprotonation. Similarly, the expand e iio-8-methyl-2-hydroxyhomotropylium ions were generated from exo- and cni/o-8-methylbicyclo[5,l,0]octa-3,5-dien-2-ones and converted into their 1-hydroxy isomers. The cncio-8-methyl-l-hydroxyhomotropylium ion underwent ring inversion to its c.xo-isomer faster than did the cnrfo-8-methyl-2-hydroxyhomotropylium ion. Irradiation of 1-acetylcyclo-octene in acetonitrile gives a mixture of the air-sensitive 3-(a-hydroxyethylidene)cyclo-octenes (248). ... 

Raney-Ni alloy added in small portions during 1.5 hrs. to a well-stirred soln. of -(2-oxocyclopentyl)butyric acid in aq. NaOH, and stirring continued 7 hrs. at room temp. -methyl-y,<5-cyclopentano-5-valerolactone (Y 98.9%) added at ca. 60° to polyphosphoric acid, and heated 5.5 hrs. at the temp, with occasional swirling under anhydrous conditions -> 4-methylbicyclo[3.3.0]-id 1.5-octen-2-one (Y 95.5%). Overall Y ca. 66%. F. e. s. T. M. Jacob and S. Dev, J. Indian Ghem. Soc. 36, 429 (1959). 

---