Chrysanthemyl derivatives

Artemisyl, Santolinyl, Lavandulyl, and Chrysanthemyl Derivatives.— The presence of (41) in lavender oil has been reported earlier. Poulter has published the full details of his work (Vol. 5, p. 14) on synthetic and stereochemical aspects of chrysanthemyl ester and alkoxypyridinium salt solvolyses (Vol. 3, pp. 20—22) and discussed its biosynthetic implications. Over 98% of the solvolysis products are now reported to be artemisyl derivatives which are formed from the primary cyclopropylcarbinyl ion (93) which results from predominant (86%) ionization of the antiperiplanar conformation of (21)-)V-methyl-4-pyridinium iodide the tail-to-tail product (96 0.01%) may then result from the suprafacial migration of the cyclopropane ring bond as shown stereochemically in Scheme 3. This is consistent with earlier work (Vol. 7, p. 20, ref, 214) reporting the efficient rearrangement of the cyclobutyl cation (94) to (96) and its allylic isomer, via the tertiary cyclopropylcarbinyl cation (95). ... 

Artemisyl, Santoiinyl, Lavandulyl, and Chrysanthemyl Derivatives.—Oxidosan-tolina triene (74) has been isolated from Artemisia tridentata together with (75), the diastereoisomer of a previously reported ester (Vol. 6, p. 20 see Vol. 7, p. 21... 

The chrysanthemyl derivative (481) has been shown to yield artemisyl and santolinyl compounds directly upon buffered hydrolysis, and this in vitro result has been presented as evidence concerning the biogenesis of these non-head-to-tail terpenoids from trans-chrysanthemyl precursors. Hydrolysis of (482) and (483) shows that head-to-head synthesis of monoterpenoids is possible from both cyclopropyl and cyclobutyl precursors. In the presence of a hydride donor such as sodium borohydride, hydrolysis of (483) gives (484) and (485) and other products in benzene-pyridine, the products are (486) and... 

Stimulated by the biogenetic proposal of Bates and Paknikar, several investigators have examined the carbonium ion reactions of chrysanthemyl derivatives 64— 73). Under acidic conditions cleavage of the bond adjacent to the unsaturated side chain in chrysanthemol (16-OH) occurs to give artemisia triene (24), a known monoterpene (64). Thus the allylic stabilization in the transition state for fragmentation... 

PouLTER has demonstrated that chrysanthemyl derivative 16-OPy I asymmetrically deuterated at the carbinyl position ionizes with 91 2% stereoselectivity from a conformation with the leaving group aligned antiparallel to the 1,3-cyclopropyl bond (68). Since rotation about the C1-C2 bond in the cyclopropylcarbinyl carbonium ion intermediate should be slow relative to nucleophilic capture, this selectivity is reflected in the position of the deuterium atom in the vinyl group of the two major products. The stereoselectivity is attributed to stabilization of the transition state for ionization by charge delocalization into the vinyl group which should be more favorable in the a/i/f-parallel alignment. Kinetic data also indicate that the double bond facilitates the ionization process. 

Unexpected results have come to light bearing on monoterpenoid biosynthesis (Chapter 1). Banthorpe s group have shown that in the formation of the thujane and camphor skeletons, activity from labelled mevalonic acid can appear predominantly in the C5 unit supposedly derived from isopentenyl pyrophosphate and only to a minor extent in the dimethylallyl pyrophosphate-derived portion. Banthorpe has also presented evidence for a chrysanthemyl intermediate, analogous to presqualene alcohol, in the biosynthesis of artemesia ketone. 

The relative stereochemistry of the substituents attached to the cyclopropane ring of presqualene alcohol received further confirmation by a synthesis of the triacetate (13), obtainable from (1) by ozonolysis, reduction, and acetylation. Treatment of 3-methyl-truns-hex-2-ene-l,6-diacetate (14) with ethyl diazoacetate in the presence of copper powder gave two isomers (15) and (16) whose stereochemistry was assigned by n.m.r. The triacetate derived from synthetic (15) by reduction and acetylation was identical in all respects with the triacetate (13) from natural presqualene alcohol. Presqualene alcohol has a c.d. curve similar to, but of opposite sign to, that of (li ,2i )-trans-chrysanthemyl alcohol (17). The mechanism for the stereospecific biosynthesis of squalene from farnesol via presqualene alcohol has received detailed comment. ... 

Car-3-ene is known to be a convenient starting material for access to the irregular chrysanthemyl skeleton (see Section 14). The (+)-olefin has been again stereo-specifically converted (via hydration and oxidation) into (+)-dihydrochrysanthemo-lactone and (+)-methyl m-chrysanthemate.667 668 Other 1,2-cis-cyclopropane derivatives have resulted from oxidative cleavage of derivatives of the same substrate.669-671... 

Certain bacteria are able to form C3Q, C45, and CgQ-isoprenoids of the phytoene type in addition to phytoene by head-to-head condensation of appropriate precursor molecules. In higher plants certain monoterpenes probably are synthesized in a similar manner. Chrysanthemyl alcohol, occurring in Compositae, is an analog of presqualene and prephytoene. The C-skeletons given in Fig. 97 are derived from chrysanthemyl pyrophosphate. Chrysanthemum carboxylic acid is a constituent of the pyrethrins, compounds with marked insecticidal activity (E 5.5.3). 

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