Ring Expansion by Three or More Carbons

Ring Expansion by Three or More Carbons.—The ra 5-divinylcyclopropanes 

R = R = H) underwent equilibration with its cis-fuscd isomer and only a trace of the cycloheptadiene was observed presumably steric interactions make the Cope rearrangement very difficult. The results suggest an initial epimeriza-tion of irons- to cis-fused isomers followed by a normal Cope rearrangement. An analysis of the kinetics of conversion of ( — )-trans-divinylcyclopropane into cyclohepta-1,4-diene indicates that the ring-opening is not a concerted pro-cess. 

The ds-divinylcyclopropanes (90 R = H or Me) are stable at room temperature and on heating undergo equilibration with their trans-isomers, rather than a Cope rearrangement.  

Related studies have been carried out with cis- and trans-divinylcyclo-butanes. The relative rates of rearrangement of the cis-divinylcyclobutanes (91 Ri = R2 = r3 = = H), (91 R = R = Me, R = R = H), (91  

181000, 41800, 1, and 435, respectively. Since the last two rates are so low these cis-isomers may be directly detected in the rearrangements of (92) and (93). A detailed analysis of the kinetics of the processes shows that rates of direct conversion of (92) and (93) into cyclo-octadienes are indistinguishable from zero.  

Ring-expansions by Three or More Carbons.— The trans,trans.trans-d y ny cyc o-propane (107) and the trans,trans,ci divinylcyclopropane (108) rearrange at 178 °C to cis- and trans-6,7-dimethylcyclohepta-l,4-diene, respectively. The cis,trans,cis-isomer (109) isomerizes to the cis,cis,cis-isomer (110) faster than to a heptadiene. The 

A key step in a synthesis of (+ )-longipinenes involved fragmentation of the hydroxy-mesylate (114 X = OMs, Y = OTHP) to the alcohol (115 Y = OTHP, Z = 

OH) when treated with lithium aluminium hydride.The cis-fused hydroxy-tosylate (114 X = OTs, Y = H) gave ketone (115 Y = H, Z = O) exclusively when treated with potassium t-butoxide whereas its trans-fused isomer gave a mixture of (115 Y = H, Z = O) and oxetan (116). The cyclodeca-1,6-diene (117) was prepared 

A synthesis of [6]paracyclophane has been reported which involves flash pyrolysis of the lithium salt of tosylhydrazone (119). Authentic samples of diketones (120) have been prepared by lead tetra-acetate oxidation of the corresponding tricyclic diols.  

Solvolysis of bicyclo[3,l,l]hept-6-yl, bicyclo[3,2,0]hept-6-yl, and bicyclo[4,l,0]-hept-2-yl dinitrobenzoates with a-methyl substituents gave product mixtures containing 20-35 % of 3-methylcyclohept-3-en-ol with a-phenyl substituents, no cyclo-heptene product was obtained. 

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