With Acids, Electrophiles, and Oxidizing Agents

With Acids, Electrophiles, and Oxidizing Agents.—Pakkanen and Whitten have studied the protonation of cyclobutane using ab initio theoretical methods. The protonation energy, 126 kcal mol was found to be similar for both edge and corner protonation. This value is significantly smaller than that found for cyclopropane. 

Acid hydrolysis of 1,1,2,2-tetra-alkoxycyclobutanes (335) gives acetals of keto-esters. The reaction is reasonably regarded as proceeding via a cationic intermediate (336), which has obvious similarities to the dipolar intermediates involved in the [2 -I- 2] additions of electron-deficient and electron-rich olefins. 

Tetrahedron Letters, 1975,445 T. Sasaki, K. Kanematu, and A. Kondo, Tetrahedron, 1975,31, 2215. 

Hexamethyl-Dewar-benzene reacts with sulphur dioxide, in presence of antimony pentafluoride, to give the bicyclo[2,l,l]hexenyl cation (344) which was identified by its and n.m.r. spectra. Quenching of the ion with wator or methoxide gives the tricyclic sulphone (345) and hexamethylbenzene. The sulphone could have been formed by rearrangement of the bicyclo[2,l,l]hexenyl cation to the bicyclo-[3,l,0]hexenyl cation (346). 

The hydroboration-oxidation and oxymercuration reactions of methyl photo-levopimarate have been investigated. Hydroboration and oxidation gave a mixture of the two alcohols (347) and (348). Oxymercuration of (346) gave the dienol (349). 

The rearrangement of angularly fused cyclobutanones, catalysed by triethyloxonium fluoroborate, has been applied to preparation of intermediates in diterpene alkaloid and giberellin synthesis.  

Treatment of the tricyclic ketone (165) with borontrifluoride etherate gave over 90% of a mixture of double bond isomers of the bicyclic ketone (166). The tricyclic ketone was prepared by intramolecular photocyclization of the 4-allylated cyclo-pentenone (167X rather than by the more conventional cyclization of a vinyl cyclo-hexenone. Cyclization of (167) in this fashion is a further example of the preference of 1,5-dienes for photocyclization to give bicyclo[2,l,l]hexane skeletons rather than bicy do [2,2,0] hexanes. 

Constantinescu-Simon, I. G. Dinulcscu, F. Chiraleu, D. Constantinescu, and M. Avram, Chem. Her., 

Interestingly, oxidation of (168) in dimethylsulphoxide with air and t-butoxide gave the rearranged ketone (173).  

Chromic acid oxidation of 2, 4, -tetrasubstituted cyclobutanones has given good yields of y-lactones. In appropriate circumstances, this method may be used in place 

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