SEQUENTIAL CYCLOADDITION-CYCLOREVERSION-CYCLOADDITION-COPE REARRANGEMENT WITH AN ANNELATED NORBORNADIENE AND ELECTROPHILIC DIENES - UNUSUAL [PI(2)(S)+PI(2)(A)+SIGMA(2)(A)] TRANSFORMATION OF A PENTACYCLO-[11.4.0.1(7,10).0(4,13).0(6,11)]OCTADECA-3,8,14,17-TETRAENE

• Published in: Tetrahedron Vol. 49; no. 21; pp. 4699 - 4710
• Main Authors: GRAVETT, EC, HOWARD, JAK, MACKENZIE, K, LIU, SX, KARADAKOV, PB
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier 21.05.1993
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Chemistry; Chemistry, Organic; Exact sciences and technology; Organic chemistry; Physical Sciences; Preparations and properties; Science & Technology; STEREOSELECTIVITY; MNDOC; DIELS-ALDER REACTION; CYCLO-ADDITIONS; THIOPHENE; DERIVATIVES; DOUBLE-BOND; PARALLEL; Pentacyclic compound; Five membered ring; Cope rearrangement; Cage compound; Hydrocarbon; Sulfone; Polycyclic compound; Reversible reaction; Organic anhydride; Thermal reaction; Dienone; Cycloaddition; Sulfur heterocycle; Chlorocarbon; Bicyclic compound; Conjugated dienic compound; Monocyclic compound
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/S0040-4020(01)81298-9

Hexachloronorbornadiene efficiently forms a 1:1 adduct 3 with 5,6-bismethylenenorbornene. Adduct 3 on reaction with 1,2,3,4-tetrachlorothiophene dioxide (TCTD) under mild conditions gives an SO2 bridged adduct, which loses SO2, the product cycloreverting to give 1,2,3,4-tetrachlorobenzene and an annelated cyclopentadiene 8; 8 reacts further with TCTD to give, in 1:1 ratio, two compounds (14 and 15) shown by mass, C-13 and H-1 NMR spectroscopy and single crystal X-ray structure determination to be the stereoisomeric products of a rare type of specific diene capture by TCTD. Evidence is presented that this result (and analogous examples) is best understood in terms of ''normal'' [4+2]pi cycloadditions to 8 as dienophile towards electron-deficient TCTD, followed by rapid Cope rearrangement of the SO2-bridged intermediate adducts to give the observed products. At low temperatures adduct 3 behaves as expected towards electron-deficient diene tetracyclone ; the [4+2]pi cycloadduct decarbonylates on mild thermolysis, concomitant cycloreversion also giving diene 8. At much higher temperatures in the presence of excess tetracyclone, diene 8 likewise behaves as dienophile; the carbonyl-bridged major cycloadduct decarbonylates to give an intermediate which undergoes an unusual thermally-allowed [pi2s + pi2a + sigma2a] 1,3-shift/cycloaddition, delivering a symmetrical cage-like structure 24, as indicated by mass and C-13 and H-1 NMR spectroscopy.