Synthesis and NMR Spectra of 2,3‐Dihydro‐l,3‐methanoindene Derivatives and l,2,3,5‐Tetrahydro‐l,3‐methanopentalene

A Novel Synthesis of 2,3‐Dihydro‐1,3‐­methano‐1H‐indene {(Bicyclo[2.1.1]hexeno)benzene} and Analysis of Its NMR Spectra

“…Table 1 (C) reveals that the analyses of the spectra of 11 – 16 provide coupling values very similar to those of 3 , which is also true for compounds 4 8a and 5 8b. The spectra of the Diels–Alder adducts 7 and 8 as well as those of their decarboxylation products 9 and 10 could be examined according to first order due to the lower symmetry of these compounds as compared with 3 .…”

“…On our request, Matsuura and Komatsu6b reanalyzed the spectrum of 2 and came up with coupling constants of virtually the same size as those of 4 and 5 . Only the signs published6b were different from those we had assigned to the coupling constants of 4 8a. However, analysis of the AA′MM′ spectra according to Günther1a is ambiguous as to the signs of the interactions, which is why our assignment8a and probably also that of Matsuura and Komatsu6b was only a guess.…”

“…This is made impressively evident by the valene 22 28 of azulene and the valene 23 of 1‐cyanoheptalene29 (Figure 4). Charges play only a secondary part, just the number of electrons is crucial, as is illustrated by the series consisting of 3 , the cyclopentadienyl anion 24 ,8a and the tropylium ion 25 30 (Figure 4). Finally, compounds 1 and 2 obey this rule, because their methylene carbon atoms display a chemical shift difference of 21.6 ppm (Figure 4).…”

“…Later, we prepared derivatives 4 and 5 8 of 3 and analyzed the AA′MM′ part of the AA′MM′X 2 spectra as described by Günther,1a which afforded coupling constants that were not in harmony with those of Pomerantz:7 J 2 n ,2 x = J 8 n ,8 x = –6.1 ( 4 8a) and –5.9 ( 5 8b), J 2 n ,8 n = –10.0 ( 4 8a) and –10.1 ( 5 8b), J 2 n ,8 x = J 2 x ,8 n = +0.6 ( 4 , 5 8), J 1,2 x = J 1,8 x = J 3,2 x = J 3,8 x = 2.5 ( 4 , 5 8), J 1,3 = 7.2 ( 4 8a), and 7.6 Hz ( 5 8b). Other couplings between the protons of the four‐membered rings are not resolved.…”