Synthesis and physical properties of sterically congested cycloalkenes, 1,2-di-tert-butyl-3,3,5,5-tetramethylcyclopentene and 1,2-di-tert-butyl-3,3,6,6-tetramethylcyclohexene

Two sterically congested cycloalkenes (9 and 10), congeners of tetra-tert-butylethylene, were synthesized and characterized. Oxidation of the bicyclic 1,3-dithietane 8 with dimethyldioxirane (DMD) gave the endo,endo-disulfoxide 13, thermal isomerization of which to the endo,exo-disulfoxide 15 followed by oxidation with DMD gave the trioxide 18. Heating 18 in refluxing 1,3-dimethyl-2-imidazolidinone furnished 1,2-di-tert-butyl-3,3,5,5-tetramethylcyclopentene (9) in 69% yield by a 2-fold extrusion process. The reaction of the I,g-diketone dihydrazone 23 with Se2Cl2 gave the selenadiazoline 34 and the 1,3-diselenetane 35. Heating 34 at 115-130 degrees C gave 1,2-di-tert-butyl-3,3,6,6-tetramethylcyclohexene (10), a didehydro derivative of tetra-tert-butylethylene, in 43% yield. The C=C bond in 10 is strained in degree comparable to those of most strained alkenes reported so far.