Consequences of fixing three parallel coplanar double bonds in close proximity with different geometries. Synthesis and spectral parameters of syn- and anti-sesquinorbornatriene

Thermal Isomerization of 12‐Oxa‐1,9‐dimetylhexacyclo[7.2.1.02,4.02,8.03,7.06,8]dodec‐10‐ene: A Computational Mechanistic Investigation

“…1): the O(8)-atom is placed above the plane C(9)ÀC(1)ÀC(6)ÀC(7) towards the four-membered ring. This effect is considerably stronger in the CAS(8,7)/6-31G(d) structure than in the UB3PW91/6-311G(d,p) structure, as indicated by the dihedral angle C(1)ÀC(9)ÀC (7)ÀO (8) (4) and C(6)ÀC (7) in TS6, and C(3)ÀC(9) and C(4)ÀC (7) .0 2,8 .0 3,7 .0 6,8 ]dodec-10-ene, 5c (anti) and 6c (syn), into our computational investigation (Scheme 5). In addition to 5c, 6c, 7c, and 8c, the stationary points 17, 18, and TS8 ± TS11 were calculated at the (U)B3PW91/6-311G(d,p)//(U)B3PW91/ 6-311G(d,p) and CAS(6,6)Pt2/6-31G(d)//CAS(6,6)6-31G(d) level of theory.…”

“…In contrast to the CAS result, the B3PW91 structure of 7c is planar. .0 2,8 .0 3,7 .0 6,8 ]dodec-10-ene type (5b and 5c) isomerize thermally via biradicals 11 and 17 to the quadricyclanes 12 or 5'c, respectively. Oxaquadricyclane 12 undergoes an experimentally well-established cycloreversion to the carbonyl ylide 16, which reacts in a 1,3-dipolar addition to the internal CC bond to form the bishomocubane derivative 9b.…”

“…Oxaquadricyclane 12 undergoes an experimentally well-established cycloreversion to the carbonyl ylide 16, which reacts in a 1,3-dipolar addition to the internal CC bond to form the bishomocubane derivative 9b. The lowest energy barrier for the thermal reaction of syn-hexacyclo[7.2.1.0 2,4 .0 2,8 .0 3,7 .0 6,8 ]dodec-10-ene (6c) is the conversion to the syn-sesquinorbornatriene 8c.…”

“…A ca. 3 : 1 mixture (300 mg, 1.61 mmol) of anti-(5a) and syn-1,9-dimethyl-12-oxahexacyclo[7.2.1.0 2,4 .0 2,8 .0 3,7 .0 6,8 ]dodec-10-ene (6a), obtained as reported earlier [2], was distilled at 0.001 Torr through a glass spiral (length 25 cm), which was placed in a tube oven (Heraeus RO 4/25) at 3508. The volatile material was condensed in a dry-ice/acetone-cooled trap.…”

“…Introduction. ± Some time ago, we showed that the quadricyclane ( tetracyclo[3.2.0.0 2,7 .0 4,6 ]heptane) derivatives 1, 2, and 3 can be generated as reactive intermediates in solution by metal halide elimination of appropriately substituted precursors, and could be trapped as Diels ± Alder adducts by organolithium compounds or by cyclic 1,3-dienes [1 ± 3]. Despite considerable experimental effort, we were unable to provide evidence for the existence of the remaining 2,3-dehydroquadricyclane 4 [4] [5], which, according to computational results, is the least-stable isomer within this series of compounds [3] [6].…”