The 1,5-sigmatropic hydrogen shifts and some other reactions of isodicyclopentadienes

Abstract

The deuteration of isodicyclopentadiene I has been studied. Monodeuterated I can be obtained by reacting methanol-d(,1) with lithium isodicyclopentadienide 15 in tetrahydrofuran at -78(DEGREES); the deuterium atom is incorporated into the ring largely at position 4(alpha) (endo), with lesser amounts of 4(beta) (exo) and at 3 and 5. The positions of deuterium were determined by ('1)H, ('2)H and ('13)C NMR on the dienes and on their adducts with dimethyl acetylenedicarboxylate (DMAD) and maleic anhydride, and using lanthanide induced shifts in the ('1)H spectra of these adducts. At 0(DEGREES) in ether, the use of H(,2)O or D(,2)O with 15 leads to as much as 62% of the previously undetected III-H or III-D, the latter being deuterated at the ring junction. Isomer III, which has been isolated and characterized, readily isomerizes to I at 100(DEGREES). Deuterium is located mainly at the 3 and 5 positions of I produced from III-D. By following the course of the isomerization of III-H and III-D, and the redistribution of deuterium in monodeuterated I, the kinetics of the 1,5-sigmatropic hydrogen shifts and the kinetic isotope effects in the isodicyclopentadiene isomers were studied. At 100(DEGREES), from III to II, II to I, and I to II, the rate constants (k(,H)) are: 5.84 x 10('-3); > 5.8 x 10('-2); and 1.0 x 10('-4), s('-1), respectively; the isotope effects (k(,H)/k(,D)) are: 3.3, 9.4, and 6.5, respectively. Some reactions of III were studied, in relation to those of I. III is less reactive than I toward dienophiles such as maleic anhydride, but is more reactive than I toward triplet oxygen. Reaction of tetracyanoethylene with III first forms the (2 + 4) cycloadduct 37, which then slowly rearranges to the (2 + 2) cycloadduct 38.