Cyclopropenes naturally occurring

In other cases cyclopropenes have been obtained by direct reaction of an alkyne with a diazo-compound in. the presence of a suitable catalyst. Typical of these is the reaction of ethyl diazoacetate with alkynes in the presence of copper, which is reported to lead to about 40-50 % conversion to cyclopropene per equivalent of diazo-compound. This has been applied to the synthesis of the important naturally occurring cyclopropene, sterculic acid, (66) 56) ... 

The polymerization of naturally occurring sterculic acid (2) in the presence of proton sources has been known for over 40 years and proceeds via acid-catalysed opening of the cyclopropene ring. The rearrangement of carboxylic acid 264a to lactone 265 is... 

The analysis of cyclopropane acids was reviewed by Minnikin (1978) and by Christie (1970), who also covered cyclopropene acids. Subsequently, Sebedio and Grandgirard (1989) discussed naturally occuring cyclic acids and cyclic acids formed in heated vegetable oils. Cyclic acids were the subject of a recent review (Le Quere and Sebedio, 1996). Useful information on gas chromatography (GC), mass spectrometry (MS) and high-pressure liquid chromatography (HPLC) of cyclic fatty acids can be found in books by Christie (1987, 1989). In the present chapter the aim is to concentrate on the more recent literature and those publications considered to be particularly... 

Figure 5.1 Structures of naturally occurring cyclic fatty acids. I, Cyclopropane acids a, 9,10-methylenehexadecanoic acid b, 11,12-methyleneoctadecanoic (lactobacillic) acid c, 8,9-methy-leneheptadecanoic (dihydromalvalic) acid d, 9,10-methyleneoctadecanoic (dihydrosterculic) acid. II, Mycolic (2-alkyl-3-hydroxy) acid. Ill, Cyclopropene acids a, 9,10-methyleneoctadec-9-enoic (sterculic) acid b, 8,9-methyleneheptadec-8-enoic (malvalic) acid. IV, Cyclopentenyl acids a, ll-cyclopent-2-enyl-undecanoic (hydnocarpic) acid b, 13-cyclopent-2-enyl-tridecanoic (chaulmoogric) acid c, 13-cyclopent-2-enyl-tridec-6-enoic (gorlic) acid. V a, 11-cyclohexyl-undecanoic acid b, 11-cycloheptylundecanoic acid.

Another group consists of cyclic fatty acids with saturated or unsaturated three-membered, five-membered and six-membered rings. The naturally occurring acids usually have the cyclopropane (3-24) or cyclopropene (3-25) ringin the middle ofthe hydrocarbon chain. The cyclopentene ring (3-26), as is the case of chaulmoogric... 

The absolute configurations of two sorts of naturally occurring compounds have been determined by X-ray crystallography, and structures of synthetic compounds, all of which contain cyclopropane groups. Compound (4) has been reported as a bisnorcaradiene with a particularly long C-1—C-6 bond (1.80 A). This non-aromatic structure for (4) corroborates earlier n.m.r. work. The cyclopropene moiety of the benzocyclopropene (5) has been shown ... 

Li, L.N., H. Li, R.W. Lang, T. Itoh, D. Sica, and C. Djerassi Minor and Trace Sterols in Marine Invertebrates. 31. Isolation and Structure Elucidation of 23 H-Isocalysterol, a Naturally Occurring Cyclopropene. Some Comparative Observations on the Course of Hydrogenolytic Ring Opening of Steroidal Cyclopropenes and Cyclopropanes. J. Am. Chem. Soc. 104, 6726 (1982). 

Li, N.L., Li, H.-T., Lang, R.W., Itoh, T., Sica, D., and Djerassi, C. (1982) Minor and trace sterols in marine invertebrates. 31. Isolation and structure elucidation of 23 H-isocalysterol, a naturally occurring cyclopropene. Some comparative observations on the course of hydrogenolytic ring opening of steroidal cydopropenes and cyclopropanes. J. Am. Chem. Soc., 104, 6726-6732. 

The 7,7-dihalobicycloheptene route appears easily adaptable to the synthesis of 6n 5 atom cyclopropa[c]heteroarenes 61 as the three-membered ring is suitably located and the requisite precursors—the dichlorocarbene addition products of, for example, 2,5-dihydrofuran—are easily accessible. Unfortunately, treatment of halides 59 with r-BuOK fails to provide any evidence for sought after 61. Dehydrochlorination does occur but the strained 1,3-bridged cyclopropenes 60 ring expand to carbene or add a nucleophile faster than rearrangement and loss of a second molar equivalent of HCl. The precise outcome of these reactions is very dependent upon the nature of the ring system as the detailed studies show . ... 

Fatty acids with trans or non-methylene-interrupted unsaturation occur naturally or are formed during processing for example, vaccenic acid (18 1 Hr) and the conjugated linoleic acid (CLA) rumenic acid (18 2 9tllc) are found in dairy fats. Hydroxy, epoxy, cyclopropane, cyclopropene acetylenic, and methyl branched fatty acids are known, but only ricinoleic acid (12(/f)-hydroxy-9Z-octadecenoic acid) (2) from castor oil is used for oleochemical production. OUs containing vernolic acid (12(5),13(/ )-epoxy-9Z-octadecenoic acid) (3) have potential for industrial use. 

Whilst the potential for synthesis of cyclopropene under volcanic conditions on primeval earth is recognized , the extent to which the ring system occurs in nature is known for only four classes of compounds, one of which involves cyclopropenone derivatives. Plants of the order Malvales contain varying amounts of the biologically active and homologous cyclopropene fatty acids sterculic acid (2) and malvalic acid (3). The... 

Gold(I)-catalysed ring-opening of 3,3-disubstituted cyclopropenes (249) with thiols, thiophenols, and thioacids has been shown to occur regio- and chemo-selectively, producing either vinyl thioethers (250) or primary allylic thioesters (251), depending on the ligands coordinated to Au and the nature of the nucleophile. ... 

---