Halogenated Monoterpenoids

Halogenated Monoterpenoids.—A separate section is devoted this year to halogen-ated monoterpenoids twenty-four acyclic and four cyclic compounds in this class have been reported. A review of halogenated monoterpenoids and sesquiterpenoids has been published.151 

The structures which have been elucidated so far may be grouped into two general categories the first group possesses the 5,6-dichloro-2,6-dimethylocta-l,3,7-triene structure (61 R = Me, X = H) with additional halogen substituents in the dimethylal-lyl pyrophosphate-derived methyl carbon atoms, and the second group has the 

Rivista Ital. Essenze-Profumi, Piante Offic., Aromi, Saponi, Cosmet., Aerosol1975, 57, 181. 

Y = Br). Two halogen-substituted ethyldimethylcyclohexanes and two halogenated furanoid monoterpenoids are reported in later sections. 

Details of the preparation of methyl (-)-cis-chrysanthemate from (+)-car-3-ene have appeared (Vol. 5, p. 15 is misleading).159 Both ( )-cis- and (+)-trans-chrysanthemic acids are again reported from (+)-car-3-ene via ozonolysis 160 this work is very similar to that reported (Vol. 5, p. 15) by Sukh Dev and illustrates the lamentable delay from receipt to publication in some journals. The decomposition of ethyl diazoacetate in 2,5-dimethylhexa-2,4-diene in the presence of the chiral copper complex (72) leads to cis- and frvms-chrysanthemic acids in 60—70% optical yield the degree of asymmetric induction is dependent upon the steric bulk of R1 and R2 in (72).161 cis-Chrysanthemic acid has also been prepared from 3,3-dimethylcyclopropene, isoprene, and 2-methylpropenylmagnesium bromide followed by treatment with carbon dioxide.162 

Halogenated Monoterpenoids.—The structures of some halogenated monoterpenoids previously reported are in error. From Aplysia californica and Plocamium coccineum, two compounds reported have structures (61 X = CHBr2) [not as Vol. 4, p, 12, formula (44)] ° and (62) [not as Vol. 4, p. 12, formula (42)] one previously reported compound has not in fact been isolated to date [Vol. 4, p. 12, formula (43)] and base treatment of compound (62) yields the epoxide (63) [not Vol. 5, p. 13, formula (53)]. °  

A new halogenated monoterpenoid from Aplysia californica is (64) which is related to the previously reported (65) (Vol. 6, p. 20), although the latter probably has a different stereochemistry the previously reported (Vol. 6, p. 20) dibromotrichloro-monoterpenoid can now be assigned the structure (61 X = CH2Br) and a third new compound may tentatively be assigned the structure (66).  

New cyclic halogen-containing monoterpenoids include plocamene C (74) (c/. Vol. 6, p. 33). No structural details were available in the abstract. This compound is closely related to violacene 2 (75) which was isolated from Plocamium violaceum the structure, determined by X-ray analysis, was inadvertently omitted from last year s Report. Chondrococcus hornemanni has also yielded chondrocole C (76), and the related tentative structure (77) has been assigned to a second component.  

Ichikawa, Y. Naya, and S. Enomoto, Proc. Japan Acad., 1975, 51, 562 Y. Naya, Y. Hirose, and N. Ichikawa, 10th International Symposium on the Chemistry of Natural Products, Dunedin, New Zealand, 1976, Abstract E32. 

Crews and E. Kho-Wiseman, 172nd A.C.S. Meeting, San Francisco, August 1976, Abstract ORGN, No. 82. 

Takabe, N. Ike, T. Katagiri, and J. Tanaka, Nippon Kagaku Kaishi, 1977, 1253. 

297 p in Marine Natural Products Chemistry , ed. D. J, Faulkner and W. H. Fenical, NATO 

Conference Series IV, Marine Sciences, Vol. 1, Plenum Press, New York, 1977 (Proceedings of a conference on Marine Natural Products, Jersey, Channel Islands, October 1976), p. 211. Formulae (8) and (13) in this paper are identical, which may suggest an error. 

Crews and E. Kho-Wiseman, J. Org. Chem., 1977, 42, 2812 formula (20) of this paper should have a chlorovinyl group instead of a 2-chloroethyl group. Plocamene B and plocamene D are reported here without comment, with absolute stereochemistry the same as violacene 2 (cf. refs. 297, 300). 

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Pyranoid monoterpenoid alkaloids have been reviewed, " and halogenated members of this class, (84) and (85), have already been discussed in the halogenated monoterpenoids section. " " The monoterpenoid ether (245) is reported from Artemisia tridentata-, from reported mass spectral data it may well be identical with the previously reported (and uncited) arthole (Vol. 7, p. 20), the characterization of which is still not published. Loliolide (246) is claimed to be an in vivo carotenoid degradation product in Canscora decussata additional spectral data have been published. ... 

Dembitsky VM, Tolstikov (1999) Natural Halogenated Monoterpenoids. Chemistry for the Interests of Stable Development 7 601 (in Russian)... 

Dimethylethylcydohexanes.—Two new halogenated monoterpenoids are violacene (150) from Plocamium violaceum,250 a 1,4-dimethyl-1-ethylcyclohexane which can be rationalized biosynthetically from the cyclization of an acyclic precursor via a bromonium ion, and plocamene B (151), again from Plocamium violaceum, which may be the first member of a series of non-isoprenoid monoterpenoids from this species.251... 

The halogenated monoterpenoids (239) and (240) have been isolated from Chondrococcus hornemanni as mentioned in the section on halogenated monoterpenoids.156 The antibiotic nectiapyrone (241) is unusual in being isolated from a... 

Red algae contain highly halogenated monoterpenoids such as 114, which is an antifeeding constiment isolated from Plo-camium cartilagineum (34, 35). 

Tetramethylcyclohexanes.—Six new esters of ferulol (162) have been detected in Peucedanum luxurians and spectroscopic evidence is provided for the presence of (163) as an ether group in the two new coumarins, iselin and iliensin, from Seseli iliense A halogenated member of this class is discussed in the halogenated monoterpenoids section. ... 

Several new fascinating halogenated monoterpenoids, e.g. (20) and (21), have been isolated from red algae of Chondroccus species their structure suggests formation by enzymic addition of BrCl to myrcene followed by dehydrohalogena-tion. 

Literature available only as a Chemical Abstract after September 1st 1978 is not, however, included. Naturally occurring halogenated monoterpenoids have been placed in a new section this year. Since many of them are now known to be cyclic compounds, it is no longer logical to classify them in the acyclic section. Non-naturally occurring halogenated monoterpenoids, however, continue to be reported in their respective sections. 

The past year has seen further advances in the isolation and characterization of new compounds, with most progress being in the area of cyclic halogenated monoterpenoids. The only new acyclic example is (89) from Aplysia limacina. ... 

Further work (c/. Vol. 8, p. 30) has indicated the considerable geographic variation in the halogenated monoterpenoid content of P. cartilagineum. Both plocamene B (96) and violacene (2) exhibit growth inhibition against mosquito larvae,and antibacterial activity against Staphylococcus aureus has been reported for ochtodene (92 X = Cl, Y = Br)." "... 

N.m.r. spectroscopy has been used extensively in the structural elucidation of halogenated monoterpenoids e.g. refs. 424,426,427) two further papers which report useful data concern C n.m.r. y-effects and the differentiation of some brominated carbons from chlorinated carbons due to shortened C n.m.r. spin-relaxation times and reduced values of nuclear Overhauser enhancement. 

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