Sesquiterpenoids. Part XV. Conformation of humulene: X-ray analysis of the crystal structure of humulene diepoxide

Abstract

The crystal structure of the title compound has been elucidated by the symbolic addition procedure and the eleven-membered carbocyclic ring of the sesquiterpene shown to have the conformation previously reported for the humulene molecule in the humulene-silver nitrate adduct, the mean deviation between corresponding torsion angles in the two molecules being 8' . Crystallographic data for the diepoxide are a = 15-265(10), b = 5.794(3), c = 16.055(8) A, p = 103' 24(4)', Z = 4, space group P2,/c. Diffractometer (Mo-K, radiation) and photographic (Cu-K, radiation) intensity data were merged to give 11 27 lFol values, and least-squares adjustment of the atomic co-ordinates and thermal parameters converged a t R 7.5%. THE sesquiterpene humulene2(1) has an elevenmembered triene ring which undergoes interesting transannular reactions, e.g. the tricyclic compounds cc-caryoyhyllene alcohol (2) and humulene bromohydrin (3) are produced by treatment of the hydrocarbon with sulphuric acid and N-bromosuccinimide,* respectively, Humulene forms a bis(si1ver nitrate) adduct,5 and X-ray analyses of this adduct established the trans-stereochemistry of all three double bonds in the hydrocarbon.6~~ The complexed hydrocarbon in the adduct has the conformation (4), and transannular cyclisations of this conformation rationalize the stereochemistries of products t No reprints available.

Humulene triepoxide

“…l) is consistent with NMR data and has a very similar conformation to the related 1,2-8,9 diepoxide (Cradwick, Cradwick & Sim, 1973) from which it can be synthesized. This constancy of conformation supports the suggestion of Cradwick, Cradwick & Sim (1973) that humulene, although a liquid at room temperature, has a preferred conformation. This constancy of conformation supports the suggestion of Cradwick, Cradwick & Sim (1973) that humulene, although a liquid at room temperature, has a preferred conformation.…”

Organotransition Metal Chemistry of Terpenes: Syntheses, Structures, Reactivity and Molecular Rearrangements

“…Of course, there have been enormous technological improvements, such as more powerful rotating anode X-ray sources, more sensitive charge-coupled or area detectors, infinitely better computational facilities, and modern direct method programs, but many common mono- or sesqui-terpenes are low-melting and volatile, characteristics that enhance their role in perfumery. The currently available structures of such materials are frequently based on crystallizable derivatives, such as the humulene complex with silver nitrate [ 123 ], or as its di-epoxide ( Figure 5 ) [ 93 ]. This difficulty has been largely overcome recently by the application of the crystalline sponge method, whereby the compound of interest is included as a guest into a porous metal organic framework consisting of, for example, ZnI 2 and 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine.…”

“…Epoxidation of humulene posed a particular problem when there was a need to functionalise only at C(3)–C(4), the least reactive double bond, because epoxidation occurs preferentially at C(1)–C(2), the most strained alkene linkage, and then at C(8)–C(9), as shown in the X-ray crystal structure of the di-epoxide ( Figure 5 ) [ 93 ]. This difficulty was finally overcome [ 94 ] by first generating the tri-epoxide, 176 , by continued treatment with m -chloroperbenzoic acid, and then removing the oxygens at C(1)–C(2) and C(8)–C(9) by reaction with WCl 6 and n -BuLi, a deoxygenation reaction previously discovered by Sharpless [ 95 ], to form 177 ( Scheme 70 ).…”

Structure and Conformation of a Humulenedione from Lippia integrifolia

“…56, No. 3 In previous work on conformational analysis of humulene derivatives, the bis(AgN03) adduct of humulene (11-13), diepoxyhumulene (14), and triepoxyhumulene (15) were evaluated after X-ray diffraction studies, showing a common conformation for their macrocycle. Moreover, the study of zerumbone 2,4-dinitrophenylhydrazone by the same technique (16) discloses, for its eleven-membered ring, a conformation that differs in the region where the phenylhydrazone group is located.…”

“…int.) [M+1]+ 237 (59), 219(81), 181 (100), 165 (49), 163 (15), 127 (12), 111 (13), 109 (21), 95 (14); 'H nmr see Molecular modeling of the preferred conformation of 1.-Humulenedione [1] in a conformation close to that deduced from *H-nmr data was manually input using the Structure Input Mode of the program PCMODEL (1.0) and then minimized with the MMX-M routine on a HP Vectra ES/12 PC. The structure readily converged to the energetic minimum represented in Figure 1 (27.9 kcal).…”