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A stereospecific five-stage synthesis of (k) -cis-pyrethrolone is described, involving cis-octa-I ,3-dien-7-one as the key intermediate. The ethylene acetal of this ketone was made by a Wittig reaction, under ' salt-free ' condiditions, with vaporised acraldehyde. The overall yield for the synthesis was 21%. and it provides highly pure (*) -cis-pyrethrolone for the first time. The material is spectrally identical with a sample of natural (+) -pyrethrolone.Improved syntheses of both (rt)-cis-cinerolone and ( 5 ) -cis-jasmololone are reported. The cis-side chains are introduced by Wittig reactions or by selective hydrogenation of acetylenic intermediates.An allenic formulation, entertained for natural pyrethrolone in the early literature, is synthesised.THE keto-alcohols cinerolone (1 a), j asmololone (1 b) and pyrethrolone (lc), known collectively as rethrolones, are the alcohol components of the insecticidally active constituents of the flower-heads of Chyysanihemzmz cinerariaefolium (pyrethrum). Severally combined with chrysanthemic acid (2a) and pyrethric acid (2b), they form the six active principles (the ' pyrethrins '), cinerin I (3a), cinerin I1 (3b), jasmolin I (3c), jasmolin I1 (3d), pyrethrin I (3e), and pyrethrin II (3f).lwith a sample of naturally derived racemic pyrethrolone (pyrethrolone B-2) was based on its closely similar i.r. spectrum [that of the (&-)-tram-compound is clearly distinguishable), and the mixed m.p. of the sernicarbazone derivatives. Both cinerolone (la) and jasmololone (lb), the latter synthesised from ' leaf-alcohol ' (cis-n-hex-3-en-l-o1),4 were obtained essentially stereochemically pure with respect to their cis-side chains, but the overall yields (ca. 1%) for the syntheses werenot high. This paper describes a new synthesis of pyrethrolone (lc) which has novel features, is completely stereospecific, and provides the (&)-&-material in an overall yield,of 21%. Improved syntheses of both (&)-cis-cinerolone (1 a) and (&-) -cis-j asmololone (1 b) are also described. R RThe stereochemical detail now accepted for the pyretlirins is shown in (3). The cis-geometry of the side-chain in k0,R' a; R = Me. b; R = Et. c; R = CH=CH, natural rethrolones (1) has been established by synthesis and spectral studies.l In earlier synthetic work on rethrolones by Crombie and Harper and their collaborators this cis-side chain has been introduced, in the cases of cinerolone (la) and pyrethrolone (lc), by partial hydrogenation of acetylenic intermediate^.^^^ In the case of pyrethrolone (lc), however, which contains a sensitive cis-vinyl-diene system, the hydrogenation of conjugated enyne precursors was not as selective asWittig reaction between the phosphorane (5) derived from the bromo-ketone (4), and acraldehyde, under ' salt-free ' conditio~is,~ gave the cis-diene (6c) almost exclusively. Its configuration followed from spectral properties, and from its recovery unchanged (spectrally) after treatment with P-benzoquinone. Hydrolysis of (6c) gave the cis-diene-ketone (7c) which was both physically and sp...

Abstract-The mass spectra of the natural pyrethrins, allethrin, the chrysanthemic acid, and the rethrolonyl and rethronyl portions of the insecticidal esters are presented, and their main fragmentation pathways are discussed.THE 'PYRETHRINS' are a group of insecticidal esters isolated from the flower heads of Chrysanthemum cinerariaef0lium.l Structurally they are derived from the three alcohols cinerolone (Ia), jasmololone (Ib) and pyrethrolone (Ic), (which are known collectively as the 'rethrolones'), and the two acids chrysanthemic acid (IIa) and pyrethric acid (IIb). The three naturally occurring esters, cinerin I (IIIa), jasmolin I (IIIb), pyrethrin I (IIIc), derived from chrysanthemic acid (Ha) are grouped together as the 'pyrethrin I' esters, whereas those esters, cinerin I1 (IIId), jasmolin I1 (IIIa) pyrethrin I1 (IIIf) derived from pyrethric acid (IIb) are grouped together as the 'pyrethrin 11' esters.l

Convenient three-stage syntheses (32-35% overall) of cis-jasmone and cis-cinerone, from readily available 3-(5-methyl-2-furyl)propionaldehyde (2) are described. Wittig reactions, under ' salt-free ' conditions are used for the cis-alkenylation (ca. 12% trans is concurrently produced). Use of an ally1 Wittig reagent (3c) led to a mixture ( 2 : 3) of cis-and trans-dienes which was converted into a mixture of cis-and trans-pyrethrone, from which cis-pyrethrone was separated and characterised. Thermal rearrangement of cis-pyrethrone gave isopyrethrone.Gk-JASBIONE (6b), an odorous principle of jasmine with jasrnololone (7b), are the alcohol components of the flowers, is useful in the reproduction of jasmine fragrance. insecticidal esters of Chrysapttlzemz-lm c i ~i e r a r i a e f o l k ~z . ~ Syntheses have been describedJ1*2 but involve several There is current interest in conversion of ketones of this siages, and proceed in low overall yields ; an exception is a recent synthesis due to Buchi and W i i e ~t . ~ Cinerone (6a) and pyrethrone (6c) are degradation products of cinerolone (7a) and pyrethrolone (7cj respectively, which,

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