Conformational behaviour of medium-sized rings. Part II. Heterocyclic analogues of 5,6,7,12-tetrahydrodibenzo[a,d]cyclo-octene (1,2,4,5-dibenzocyclo-octa-1,4-diene)

Abstract

The temperature dependence of the n.m.r. spectra of a number of heterocyclic analogues (2) of 5.6,7,12-tetrahydrodibenzo[a,d]cyclo-octene has been interpreted in terms of the interconversion of chair-and boat-like conformations. These interpretations have been supported by strain energy calculations, and there is a useful correlation between the activation parameters determined by variable temperature n.m.r. spectroscopy and the results provided by these calculations. The 1 2-oxodibenz[c,f]azocine derivative (21) apparently exists preferentially in a boat conformation as a consequence of a weakly bonding interaction between N(6) and the C(12) carbonyl function.IN Part I we discussed the conformational behaviour of 5,6,11,12-tetrahydrodibenzo[a,e]cyclo-octene (1) and some heterocyclic analogues. These compounds showed temperature dependence of their n.m.r. spectra which could be associated with chair-and boat-like conformations undergoing inversion and interconversion a t relatively low rates on the n.m.r. time scale. Since this work was completed a number of papers have appeared concerning conformational studies of the hydrocarbon (1),2 some heterocyclic analogues of (I),3 the related hydrocarbon cis,~is-I,5-cyclo-octadiene,~ and its syn-3,7-dibromo d e r i ~a t i v e . ~ It is clear from these results that the lJ5-cyclo-octadiene system can show interesting conformational behaviour involving a rigid chair conformation and a mobile boat conformation.6 It is evident from the examination of models and from geometrical considerations that the 1 ,.l-cyclo-octadiene system might show similar conformational behaviour. We have therefore examined some heterocyclic analogues (2) of 5 , 6,7 , 12-tetrahydrodibenzo [a& cyclo-octene using n.m.r. line-shape methods which have been demonstrated to be a powerful technique for solving the subtle problems posed by the conformational behaviour of cyclic compounds in solution.The cyelic sulphides (2a),8 (2d), (Zg), and (Zi) were prepared by the reaction of the corresponding bis(bromomethyl) compounds (3a-d) with sodium sulphide. Bis-(2-bromomethylpheny1)methane (3a) was prepared by a published p r o c e d ~r e , ~ with slight variations as noted in the Experimental section. The bis(bromomethylphenyl) ether (3b) and sulphide (3c) were prepared by controlled side-chain bromination of the corresponding di-o-tolyl derivatives. The sulphones (2b),s (Zl), (Zj), and (3d) were readily prepared by oxidation of the corresponding sulphides with peracetic acid. The amines (2c), (Zf), (Zh), and (2k) were prepared by the reaction of the corresponding bis(bromomethy1) compound (3) with benzylamine in benzene. The -f Throughout this paper we have used the nomenclature recommended by I.U.P.A.C. rule A-21.4, as in Part I.

Reinvestigation of base-induced skeletal conversion via a spirocyclic intermediate of dibenzodithiocinium derivatives and a computational study using the HF/6-31G* basis set

“…Treatment of 2 under the same conditions (methanolic KOH) did not furnish 12, which had been expected from the rearrangement of 1, but the structural isomer 6 in 29% yield along with a small amount of 2-methoxymethylphenyl 2-methylthiomethylphenyl sulfide (7) in 5% yield which was produced by way of the ring-opening by nucleophilic substitution of 2 with methanol as shown in Scheme 3.…”

“…By means of a similar procedure to 1a, treatment of 2 (135 mg, 0.468 mmol) with 0.7 g of potassium hydroxide in 5 mL of methanol afforded 29.2 mg (29%) of 6 and 5.2 mg (5%) of 2-methoxymethylphenyl 2-methylthiomethylphenyl sulfide (7), after thin layer chromatographic separation on silica gel (n-hexane-ether; 9 : 1). For 6: mp 86-87 ЊC; 1 H NMR (δ CDCl 3 ) 2.16 (s, 3H), 4.10, 4.60 (ABq, J = 13.9 Hz, 2H), 5.42 (s, 1H) and 7.0-7.3 (m, 8H); mass (m/z) 258 (M ϩ , 7%), 211 (M ϩ Ϫ47, 100), 178 (M ϩ Ϫ-80, 68%).…”

The crystal and molecular structure of 6-(1,1-dimethylethyl)-12,12-dimethyl-5,6-dihydro-7H,12H-dibenzo[c,f][1,5]silazocine

“…The central ring in the title compound adopts a distorted boat conformation (Gellatly, Ollis & Sutherland, 1976) similar to that reported as twist-boat for the …”

Molecular mechanics study of transannular amine-ketone (N?C(DOUBLE BOND)O) interaction in medium-sized heterocycles

“…However, early attempts at modeling typical compounds with force-field based and semiempirical molecular-orbital based methods 15 and this work Ž . demonstrated see later that the N ª C O interaction is not reproduced satisfactorily by these calculations.…”