Humulenes

Intramolecular allylation offers a useful synthetic method for macrocyclic compounds. An application to the synthesis of humulene (83) by the cycliza-... 

Organoboranes are reactive compounds for cross-coupling[277]. The synthesis of humulene (83) by the intramolecular cross-coupling of allylic bromide with alkenylborane is an example[278]. The reaction of vinyiborane with vinyl-oxirane (425) affords the homoallylic alcohol 426 by 1,2-addition as main products and the allylic alcohol 427 by 1,4-addition as a minor product[279]. Two phenyl groups in sodium tetraphenylborate (428) are used for the coupling with allylic acetate[280] or allyl chloride[33,28l]. 

Humidity control Huminite Humoryl Humphrey spirals Humphrey s spiral a-Humulene [d753-98-d]... 

Few naturally occurring fused-ring thiiranes are known. Recently, however, humulene-1,2- and -4,5-episulfides (84) and (85), and caryophyllene-4,5-episulfide (86) were isolated from hops which had been heavily dressed with sulfur during the growing period, to control mildew (80JCS(P1)311). 

Hiickel linear combination of atomic orbitals pyridines and benzo derivatives, 2, 102 Hiickel molecular orbital method colour and constitution, 1, 342 Hugerschoff bases synthesis, 6, 475-477, 493 Humulene... 

The 11-membered ring of humulene, a major impediment to synthesis, was constructed by a novel nickel-mediated cyclization. 

Humulene is the name lassigned by Chapman to the sesquiterpene which he isolated from essential oil of hops. Its characters are as follows —... 

Humulene nitrosite, C,5H24N203, was obtained in two modifications, one forming blue crystals melting at 120°, and the other colourless melting at 166° to 168°. 

The similarity between humulene and caryophyllene had not escaped Chapman s notice at the time that he isolated humulene, but as he was nnable to prepare a hydrate, which is one of the easiest of the caryophyllene derivatives to obtain in a pure state, he concluded that the sesquiterpene was not identical with caryophyllene. Eecent work by fiemmler does not tend to establish the identity of the two sesquiterpenes, and unless and until further evidence to the contrary is forthcoming, humvdene may be regarded as a definite chemical individual. 

Regardless of Llieu apparent structural differences, all terpenoids are related. According to a formalism called the isoprene rule, they can be thought of as arising from head-to-tail joining of 5-carbon isoprene units (2-methyl-1,3-butadiene). Carbon 1 is the head of the isoprene unit, and carbon 4 is the tail. For example, myreene contains two isoprene units joined head to tail, forming an 8-carbon chain with two 1-carbon branches. a-Pinene similarly contains two isoprene units assembled into a more complex cyclic structure, and humulene contains three isoprene units. See if you can identify the isoprene units in a -pinene and humulene. 

Humulene. structure of, 202 Hund s rule, 6 sp Hybrid orbitals. 17-18 sp2 Hybrid orbitals, 15. sp3 Hybrid orbitals, 12-14 Hydrate, 701... 

Martin et al. (1974) collected specimens from 22 locations throughout the range of H. courbaril and identified a number of sesquiterpenes including caryophyllene [173], humulene [174], selinene isomers [175 is P-selinene], and other related compounds (see Eig. 2.48 for compounds 173-175). Caryophyllene and two selinene... 

Variation within a species was examined by looking at the chemistry of Z. dipetalum specimens collected from sites on three islands, Hawaii, Kauai, and Oahu. Of the seven compounds detected in this comparison, only two, caryophyl-lene [542] and humulene [543] (see Fig. 6.5 for structures 542-546), were present in all individuals. Trees from a site on Oahu were unique in their possession of... 

Sampling time 60 min extraction temperature 80°C. Monoterpenes a-pinene, p-myrcene, a-phellandreneand limonene sesquiterpenes a-cubebene, a-copaene, p-elemene, p-caryophyllene, a-humulene, y-muurolene, p-eudesmene and caryophyllene oxide diterpenes cembrene A and isoincensole acetate. 

The first observation is the similarity between the chemical compositions of both the Boswellia carteri and Boswellia sacra. For these three olibanum samples, a-pinene (2), (3-myrcene (8) and limonene (14) are the predominant monoterpenes. p-Caryophyllene (73) is the major sesquiterpene besides a-copaene (65), a-humulene (also called a-caryophyllene) (78) and caryophyllene oxide (95). The characteristic olibanum compounds isoincensole and isoincensole acetate (128) together with cembrene A (120) are the main diterpenes. 

Boswellia serrata olibanum has a chemical composition close to that of both the B. carteri and of B. sacra, but contains compounds that are absent in those from other Boswellia and could be used as markers methylchavicol (38), p-anisaldehyde (47), methyleugenol (70), isocaryophyllene (82), sesquiterpene 91, elemicin (92) and an unidentified diterpene (124) eluting between cembrene C (123) and verticilla-4(20),7,ll-triene (125). It is devoid of (5-caryophyllene (73), a-humulene (78), caryophyllene oxide (95) and bornyl acetate (50). 

Eight olibanum samples of unknown botanical origin have been analysed [26]. The chemical compositions are summarized in Table 10.3 for three of them. Both the olibanum coming from Somalia and that from a market in Ta izz (Yemen) have been attributed to Boswellia carteri or sacra on the basis of the occurrence of the characteristic diterpenes isoincensole and isoincensole acetate (128) together with diterpene 126. The absence of methylchavicol (38), oxygenated sesquiterpene 91 and diterpene 124 and the presence in relatively large amount of (3-caryophyllene (73), ot-humulene (78) and caryophyllene oxide (95) excluded the hypothesis of a B. serrata sample. 

Dicarbonyl coupling (8,483). This Ti-catalyzed coupling offers a useful route to cyclic sesquiterpenes such as humulene (4). The precursor is obtained by coupling a vinylic zirconium compound (1) with the u-allylpalladium complex (2) to give, after deprotection, the keto aldehyde 3 in 84% yield. This product couples to humulene as a single isomer in 60% yield. 

A quite detailed review of transannular cyclizations was published201 wherein their important role in biomimetic syntheses of sesquiterpenes as well as explanation of the biogenetic formation of the polycyclic natural compounds from their monocyclic precursors is discussed. The great significance of these transformations for the synthesis of natural products is also emphasized in a series of reviews which describe the cyclizations to form terpene derivatives, e.g., of the germacrane and humulene systems202-206. 

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