Synthesis and properties of sterically hindered cycloalkenes carrying two tert-butyls in Cis orientation. 2,3-Di-tert-butylbicyclo[2.2.2]oct-2-ene derivatives

Article abstract of DOI:10.1021/ja00177a028

3,4-Di-tert-butylthiophene 1,1-dioxide (2), a cheletropic Diels-Alder reagent, reacts with 2 molecules of maleic anhydride to give the endo-endo bisadduct 4a (73%) and endo-exo bisadduct 4b (23%), which have a highly hindered double bond incorporated in a bicyclo[2.2.2]oct-2-ene ring system. The reaction of 2 with 2 equiv of PTAD affords the bisadduct 7 (87%). which is directly converted to 4,5-di-tert-butylpyridazine in 80% yield by treatment with KOH/MeOH followed by air oxidation and nitrogen extrusion. The reaction of 2 with phenyl vinyl sulfone affords o-di-ferf-butylbenzene in 89% yield with loss of sulfur dioxide and benzenesulfinic acid. Reduction of 4a and 4b with LiAIH₄ followed by treatment of the resulting tctrols with p-toluenesulfonic acid affords the ether derivatives 15a and 15b, respectively, in good overall yields. The double bond of these hindered cycloalkenes is inert to hydroboralion, peracid oxidation, and singlet oxygen, but both 15a and 15b react with bromine to give yellow, unstable crystalline 1:1 adducts to which we propose the polymeric either-bromine adduct structure 19 rather than the bromonium bromide structure 18.