Competition between Cheletropic and Homocheletropic Additions of Sulfur-Dioxide to 2,3,5,6-Tetrakis(Methylene)Bicyclo[2.2,N]Alkanes - Crystal and Molecular-Structures of 2 3-Thiabicyclo[3.1.0]Hexane 3,3-Dioxide Derivatives

At -20 degrees C, SO2 undergoes homocheletropic addition with 7,7-dimethyl[2.2.1]hericene (18) to give (1R,5S)-6,10-dimethylidene-8-isopropylidene-3-thiatetracyclo[5.2.1.0(1,5 ).0(5,9)]decane 3,3-dioxide (21). This 3,3-dioxide (21). This sulfolane Is isomerized into (IR, 7S)-8,9-dimethylidene-10-isopropylidmte-4-thiatricyclop[5.2.1.0(2,6)]dec -2(6)-ene 4,4-dioxide (22). At 20 degrees C, the equilibrium ratio;[21]/[22] = 4:1, the sulfolane being slightly more stable than the isomeric sulfolene, in contrast with the reactions of SO2 with 2,3,5,6-tetramethylidenebicyclo[2.2.1]heptane and 5,6, 7,8-tetramethylidenebicyclo[2.2.2]oct-2-ene. While 2,3,5, 6, 7-pentamethylidenebicyclo,[2.2.2]octane (19) and [2.2.2]hericene (20) react with SO2 to give first the corresponding monosulfolenes (1SR,7RS)-8,9,10-trimethylidene-4-thiatricyclo[5.2.2.0(2,6)] undec-2(6)-ene 4,4-dioxide (24) and 8,9,10,11-tetramethylidene-4-thiatricyclo[5.2.2,0(2,6)]undec-2(6)-ene 4,4-dioxide (27) respectively, these adducts undergo homocheltropic additions concurrently with the cheletropic additions of SO2 under conditions of kinetic control, giving (1SR, 2SR, 8RS, 10SR)-9-methylidene-5,12-dithiapentacyclo[6.5.1.0(1,1)0.0(3,7)]tetradec- 3(7)-ene 5,5,12,12-tetraoxide (25) and (1R,10S)-9.14-dimethylidene-5,12-dithiapentacyclo[6.5.1.0(1,10).0(2,10). 0(3,7)]tetradec-3(7)-ene 5,5,12,12-tetraoxide (28), respectively. At 20 degrees C 25 was partly isomerized into the bissulfolene 13-methylidene-4,10-dithiatetracyclo[5.5.2.0(2,6).0(8,12)]tetradeca-2(6) , 8(12)-diene 4,4,10,10-tetraoxide (26) ([25]/[26] = 2:1), whereas 28 was completely converted to the move stable bissulfolene 13,14-dimethylidene-4,10-dithiatetracyclo-[5.5.2.0(2,6).0(8,12)]tetradec a-2(6), 8(12)-diene 4,4,10,10-tetraoxide (29). Single crystal X-ray diffraction studies on 6,6-dimethyl-3-thiabicyclo[3.1.0]hexane 3,3-dioxide (4) and 6,11-dimethylidene-3-thiatetracyclo-[5.3.1.0(1,5).0(5,10)]undec-8-ene 3,3-dioxide (12) revealed unusual bond elongations for the sigma bond connecting C(1) and C(5) in 3-thiabicyclo[3.1.0]hexane 3,3-dioxide systems.