Conformational study of a series of 6-substituted 5,6,7,12-tetrahydrodibenzo[a,d]-cyclooctenes by nuclear magnetic resonance spectroscopy

Abstract

Can. J. Chem. 55,3456 (1977). The conformational properties of seven 5,6,7,12-tetrahydrodibenzo[a,d]cyclooctenes bearing substituents at C-6 have been studied using variable temperature proton nmr spectroscopy. The position of the equilibrium between boat-chair (BC) and twist-boat (TB) conformers has been measured in several solvents. In contrast to the unsubstituted dibenzocyclooctene, appreciable amounts of TB conformer are present when C-6 is substituted by alkyl, hydroxy, or cyano substituents. Measurements at different temperatures showed the TB form to possess the greater entropy. Barriers to the BC + TB interconversion were determined by coalescence studies, using both approximate and complete line shape methods. Barriers ranged from 10.1 kcal/mol for the 6-keto derivative to 16.7 kcal/mol for the 6-hydroxy-6-methyl derivative. Chem. 55,3456 (1977). ROGER N. RENAUD, JOHN W. BOVENKAMP, ROBERT R. FRASER et JEAN-LOUISOn etudie, par resonance magnktique du proton (rmn) et variant la temperature, les propriktts conformationnelles de sept tetrahydro-5,6,7,12 dibenzo[a,d]cyclooctenes ayant des substituants en C-6. La position de l'tquilibre entre les conformeres chaise-bateau (CB) et bateau-crois6 (BC) est mesuree dans plusieurs solvants. Contrairement au dibenzocyclooctene non substitue, une quantite appreciable de conformeres (BC) est prtsente lorsque le C-6 est substitue par un groupe alkyle, hydroxy ou cyano. Les mesures a differentes temperatures montrent que la forme BC possede une plus grande entropie. Les barrieres d'interconversion CB + BC sont dttermintes par des etudes de coalescence en utilisant les methodes approximatives et completes basees sur la forme des courbes. Les barrieres s'ktalent de 10.1 kcal/mol pour le derivt cCto-6 a 16.7 kcal/mol pour le derive hydroxy-6 methyl-6.[Traduit par le journal] I n the past few years the dibenzocycloocta-1,4-diene3 ring system l a has attracted considerable interest regarding its conformational properties. The first evidence on this topic came from a 'H nmr study of compounds related to la, specifically the azocines 2a-f (1, 2). Subsequently studies on a variety of other heterocyclic analogs 3a-1 were reported (3) and, most recently, the conformational properties of the hydrocarbon l a itself have been described (4). The parent compound, 1,4-cyclooctadiene, has been the subject of analysis by I3C and 'H tech-'NRCC No. 16120. 2Present address: Defence Research Establishment Ottawa, Ottawa, Ont., Canada KIA 024.3The eight-membered ring l a , whose correct name is 5,6,7,12-tetrahydrodibenzo[a,d]cyclooctene, has the numbering shown in formula 1. This numbering is employed throughout the paper. niques (5) as well as by strain energy or force field calculations (5, 6). In this paper we wish t o describe the elucidation of the conformational properties of a series of dibenzocyclooctadiene derivatives lb-h (7) by the use of 'H nmr techniques. For personal use only.

Steric Consequences on the Conformation of Medium-Sized Rings: Solution NMR, Solid-State Crystallographic, ab Initio Molecular Orbital Calculations, and Molecular Mechanics Studies on Substituted Eight-Membered Organosilicon Ring Systems1

“…The originally observed dependence for the geminal 2 J HCH coupling constant of the C( 12)-geminal protons in substituted 5,6,7,12-tetrahydrodibenzo [a,d]cyclooctenes with ring conformation [45][46][47][48] was extended to probe the conformation of 12Hdibenzo[d,g][1,3,2]dioxaphosphocins in solution. 6e,f,8a,b The observation of a geminal coupling constant of -12 to -13 Hz in 12H-dibenzo[d,g][1,3,2]dioxaphosphocins is consistent with a BC (or BB) conformation with the exocyclic substituent on phosphorus assuming a pseudoequatorial placement, whereas TB and B conformations were associated with coupling constants ranging from -14 to -19 Hz.…”

Phosphorylation of p-tert-butylthiacalix[4]arene: reaction with phosphorous triamides

“…1). In Scheme 2, a simplified transformation scheme of the eight-membered ring conformers of 3 is shown, which 13 and investigated by Arshinova and co-workers. 14 Because of the NOE effects 5b/1aЈ,bЈ > 5bЈ/1a,b, it is obvious that one of the phosphocine rings of 3 represents an equatorial boat-chair (e-BC) conformation with a 31 P NMR shift of 140.4 ppm for the 1Ј-P atom undergoing a fast conformational change to the axial distorted-twist-boat (a-DTB) conformation as indicated by the 4Ј,6Ј/1bЈ crosspeaks.…”

“…The 31 P NMR shifts were assigned by the 2D-31 P/ 1 H-HOESY and 1 H/ 31 P-HMBC methods, respectively. The 14-P atom of 4 gives a shift at 141.5 ppm, the Scheme 2 Conformational transformations of the two different thiaphosphocine fragments of the phosphorus thiacalixarene 3 according to Renaud et al 13 and the NOE effects observed (volume integrals A ij ).…”

Synthesis and Conformation of Chiral Eight-Membered 12H-Dibenzo[d,g][1,3,2]dioxaphosphocins1

“…The originally observed dependence of the magnitude of the couplings of the C(12) geminal protons in substituted 5,6,7,12-tetrahydrodibenzo[ a,d ]cyclooctenes upon ring conformation − was extended to probe the conformation of 12 H -dibenzo[ d,g ][1,3,2]dioxaphosphocins in solution. − The observation of a geminal coupling constant of −12 to −13 Hz with observable 5 J HP coupling of 2−4 Hz in 12 H -dibenzo[ d,g ][1,3,2]dioxaphosphocins is consistent with a BC conformation with the exocyclic substituent on phosphorus assuming a pseudoequatorial placement . Both the magnitude of the observed coupling constants and the observation of 5 J HP suggest that 7 and 8 assume a biased BC conformation in solution with a pseudoequatorial substituent on phosphorus.…”

“…38 The B conformation is characterized by a C aromatic -O-P-O torsion angle of 0°. 34 The originally observed dependence of the magnitude of the couplings of the C(12) geminal protons in substituted 5,6,7,12-tetrahydrodibenzo[a,d]cyclooctenes upon ring conformation [41][42][43][44] was extended to probe the conformation of 12H-dibenzo[d,g][1,3,2]dioxaphosphocins in solution. [34][35][36][37] The observation of a geminal coupling constant of -12 to -13 Hz with observable 5 J HP coupling of 2-4 Hz in 12H-dibenzo[d,g]-[1,3,2]dioxaphosphocins is consistent with a BC conformation with the exocyclic substituent on phosphorus assuming a pseudoequatorial placement.…”