Longifolene derivatives

Several papers on the chemistry of longifolene derivatives have been published. These include the conversion of the two half-esters (225) and (226) into the same olefinic ester (227) with Pb(OAc)4-Cu(OAc)2, the reaction of longifolene (228) with mercuric acetate followed by iodine chloride to give (229) and (230), and the reaction of longicyclene (231) with bromine in pyridine and iodine chloride-pyridine complex in acetic acid to yield (232) and (233) respectively. 

VIII. Ultraviolet Absorption of Some Longifolene Derivatives. 95... 

Among chiral dialkylboranes, diisopinocampheylborane (8) is the most important and best-studied asymmetric hydroborating agent. It is obtained in both enantiomeric forms from naturally occurring a-pinene. Several procedures for its synthesis have been developed (151—153). The most convenient one, providing product of essentially 100% ee, involves the hydroboration of a-pinene with borane—dimethyl sulfide in tetrahydrofuran (154). Other chiral dialkylboranes derived from terpenes, eg, 2- and 3-carene (155), limonene (156), and longifolene (157,158), can also be prepared by controlled hydroboration. A more tedious approach to chiral dialkylboranes is based on the resolution of racemates. /n j -2,5-Dimethylborolane, which shows excellent enantioselectivity in the hydroboration of all principal classes of prochiral alkenes except 1,1-disubstituted terminal double bonds, has been... 

Other examples of chiral organoboranes derived from terpenes are E, F, and G, which are derived from longifolene,198 2-carene,199 and limonene,200 respectively. 

The synthesis in Scheme 13.30 was also done in such a way as to give enantiomer-ically pure longifolene. A starting material, whose chirality is derived from the amino acid L-proline, was enantioselectively converted to the product of Step A in Scheme 13.30. 

Fig. 5-3. Examples of mono- and sesquiterpenes and their derivatives in softwood. 1, a-Pinene 2, /3-pinene 3, 3-carene 4, camphene 5, borneol (R = H), bornyl acetate (R = COCH3) 6, limonene 7, a-terpineol 8, dipentene 9, a-muurolene 10, 8-cadinene 11, a-cadinol 12, a-cedrene 13, longifolene 14, juniperol.

For other 6-substituted derivatives, the proportions of the two products were reversed when zinc(II) chloride in methanol, or chromium(II) sulfate in aqueous dimethylformamide, was used as reductant. Lithium/ammonia reduction of ethyl 5-oxotetracyclo[5.4.0.0 . 0 ]un-dec-lO-ene-8-carboxylate (30) gave a higher proportion of the sinularene-type product, ethyl 2-methyl-4-oxotricyclo[4.4.0.0 ]decane-7-carboxylate (31), than the longifolene-type, ethyl 5-oxotricyclo[5.4.0.0 ]undecane-8-carboxylate (32). Once again, these proportions were reversed for other 8-substituted substrates when zinc metal/zinc(II) chloride in methanol, or chromium(II) sulfate in aqueous dimethylformamide, was used to induce cyclopropane cleavage. ... 

Previously Arigoni210 had put forward an elegant stereochemical argument for the co-occurrence of (—)-longifolene (432) and (—)-sativene (433) from this fungus, as summarized in Scheme 56. The detection of (431) in the mycelium adds substantial support to this proposal since it is the very ten-membered ring intermediate en route to (—)-sativene. The final verification of the structure of (431) was achieved by carbanionic cyclization of the, cis,trans-fa.mesy sulphide (434) followed by reductive removal of the sulphide group and dehydration of the derived tertiary alcohol. 

Olefin cyclization (3, 305-307 4, 531-532 5, 696-697). A key step in a novel synthesis of ( )-longifolene (6) from (1) involves the acid-catalyzed cycUza-tion of (2) to (3) with TFA at 0°. The original paper suggests a mechanism for the cychzation of (2) mainly to the bicyclic product (3) rather than to a hydro-azulene derivative. ... 

The importance of the syn relationship of hydrogen and the leaving group is seen in hydrindanes 227 and 228, which produced 229 upon pyrolysis. The cis-derivative (227) required temperatures at least 200°C higher than the trans-acetate (228).209b synthetic example that involves ester pyrolysis is taken from Fallis synthesis of (-t-)-longifolene (230), formed in 56% yield by pyrolysis of 231. 10... 

Ourisson et al have shown that the alkylborane derived from hydroboration of longifolene (167) is auto-oxidized in the presence of oxygen to give the expected product (168) in about 33% yield and significant amounts of the two epimeric... 

Contents P. LEFRANCIER and E. LEDERER Chemistry of Synthetic Immunomodulant Muramyl Peptides. — SUKH DEV The Chemistry of Longifolene and Its Derivatives. — W. HELLER and CH.TAMM Homoiso-flavanones and Biogenetically Related Compounds. — R. G. COOKE and J. M. EDWARDS Naturally Occurring Phenalenones and Related Compounds. — C. W. JEFFORD and P. A. CADBY Molecular Mechanisms of Enzyme-Catalyzed Dioxygenation (An Interdisciplinary Review). 

It appears worthwhile to discuss the reactions of longifolene in terms of the above four categories, even though some reactions of longifolene are known to lead to products of more than one type. In such cases, the reaction has been discussed under only one head or both the heads, depending on whether one pathway is dominant or not. Besides these four categories of reactions, some other pertinent transformations of longifolene and its derivatives are discussed under two additional heads (i) Conversions into other sesquiterpene skeletons, and (ii) Miscellaneous transformations. 

Chart 13. Carbocations and quenching products derived from longifolene in fluorosulfonic... 

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