William Kitching

Spiroacetals in Insects

Spiroacetals, cryptic ketodiols showing a hydroxyl group at both sides of a carbonyl whithin reachable distances are very widespread in nature. A group of 30 different structures, not including stereoisomers, represent volatile, less polar constituents of insect secretions. Five different systems were identified: 1,6-dioxaspirol[4.4]nonanes, 1,6-dioxaspiro[4.5]decanes, 1,6-dioxaspiro[4.6]undecanes, 1,7-dioxaspiro[5.5] undecanes, and 1,7-dioxaspiro[5.6]dodecanes. Some spiroacetals are insect pheromones: (2S,5R)-2-ethyl-1,6-dioxaspiro[4.4]nonane, chalcogran, 1, is a key component of the male produced aggregation pheromone of the spruce bark beetle, Pityogenes cha2cographus. In contrast, (5S,7S)-7-methyl-1,6-dioxaspiro[4.5]decane, 2, conophthorin, acts as a repellent or spacer in several bark beetles. Racemic 1,7-diosaspiro[5.5]undecane, olean, 5, is the female produced sex pheromone of the olive fly, Bactrocera (Dacus) oleae. The most widespread spiroacetal is 2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 8. Tt often forms a mixture of (E,E)- and (E,Z)-isomers, the (E,E)-isomer showing (2S,6R,8S)-configuration. In the solitary bee, Andrena wilkella, it serves as an aggregation pheromone. Present knowledge on structures and distribution of volatile spiroacetals is comprehensively compiled. Stereochemical aspects and mass spectrometric fragmentation patterns are discussed in detail to facilitate identifications of hitherto unknown compounds. Synthetic approaches to spiroacetals are classified and reviewed. Last but not least, facts and speculations on the biosynthesis of volatile spiroacetals are presented.

Total Synthesis and Absolute Stereochemistry of Plakortone D

The first total synthesis of plakortone D is described and thereby establishes the structure and absolute stereochemistry of the most biologically active member of the marine-derived plakortone family. The sterically congested bicyclic lactone core results from a Pd(II)-induced hydroxycyclization-carbonylation-lactonization sequence on an enediol whose chirality was installed by AD-technology. Attachment of the side chain, also constructed using AD-methodology, was achieved by using a modified Julia coupling. The described approach enables acquisition of other plakortones and analogues, in the correct (natural) stereochemical series.

Group IVb metalloidal substituent effects studied by carbon-13 nuclear magnetic resonance spectroscopy

Abstract The natural abundance carbon-13 NMR spectra of series of compounds ArX(CH 3 ) 3 (At = phenyl, 1- and 2-naphthyl, 4-biphenyl and 9-anthryl; X = C, Si, Ge, Sn, Pb), have been recorded and essentially completely assigned by specific deuteration, magnitudes of 13 CX couplings and other criteria. For these directly bonded metalloidal systems, the substituent chemical shifts at formally conjugated positions have been considered in terms of mesomeric electron withdrawal, associated with orbitals of π-symmetry on X, and opposing electron donation, resulting from the aryl CX bond polarisation. For silicon the former effect predominates, but for germanium, tin and lead, opposing electron-donating mechanisms assume importance. For 1-naphthyl systems, the effects of molecular distortion on carbon-13 chemical shifts are critical at certain positions. The substituent effects of M(CH 3 ) 3 in aromatic systems are very feeble in comparison with the conventional substituents of organic chemistry.

Sulfur dioxide insertion into carbontin bonds: II. Rearrangements accompanying insertion☆

A number of allylic, allenylic and 2-propynylic (R′) derivatives of tin of the type R3SnR′ have been synthesized, and shown to undergo ready insertion of sulfur dioxide into the SnR′ bond. Rearrangement accompanies insertion so that the products have the alternate allylic, 2-propynylic and allenylic structures respectively. Di-insertion occurs only when groups attached to tin are quite susceptible to electrophilic cleavage. NMR data for the compounds are reported.

Carbon magnetic resonance studies of some phenyl, furyl and thienyl organometallics. Some comments on carbon-metal scalar coupling

13C chemical shift variations within a series of phenyl, furyl and thienyl Group IVB organometallics appear to be best understood in terms of the usual alkyl and aryl substituent effects on 13C chemical shifts and not variations in dπ ?pπ metal-aryl interactions. Large changes in 13C-metal scalar coupling constants have been observed suggesting that other factors besides the s-character of the carbon-metal bond is responsible in determining the coupling constant.

Chemical studies of rectal gland secretions of some species ofBactrocera dorsalis complex of fruit flies (diptera: Tephritidae).

Male-produced rectal gland secretions of a number of species now considered to be members of theBactrocera dorsalis complex of fruit flies have been examined by combined gas chromatography-mass spectrometry. The structures of a number of previously unreported compounds have been confirmed by synthesis and Chromatographic comparisons. Compounds identified in these secretions include fatty acids, esters, amides, keto alcohols, diols and spiroacetals. These chemical findings are in agreement with taxonomic revisions based on other criteria.

Steroidal saponins from the roots of Trillium erectum (Beth root).

Eleven steroidal saponins including three previously unreported saponins 1-3, two known ecdysteroids and one fatty acid, have been isolated from the roots of Trillium erectum (Beth root) by RP-HPLC and characterized by spectroscopic (1D and 2D NMR experiments) and spectrometric (LCMS) methods.

Characterisation of alkaloids from some Australian Stephania (Menispermaceae) species

Chemical investigations of some Stephania species native to Australia and reportedly employed by Aboriginal people as therapeutic agents, are described. The alkaloids from the forest vines Stephania bancroftii F.M. Bailey and S. aculeata F.M. Bailey (Menispermaceae) have been isolated and characterised. The major alkaloids in the tuber of the former species are (-)-tetrahydropalmatine and (-)-stephanine, whereas these are minor components in the leaves, from which a C-7 hydroxylated aporphine has been identified. The major tuber alkaloids in S. aculeata are (+)-laudanidine, and the morphinoid, (-)-amurine, whose absolute stereochemistry has been established by X-ray structural analysis of the methiodide derivative. No significant levels of alkaloids were detected in S. japonica. Complete and unambiguous 1H and 13C NMR data are presented for these alkaloids.

Hydrolytic kinetic resolution of terminal mono- and bis-epoxides in the synthesis of insect pheromones: routes to (-)-(R)- and (+)-(S)-10-methyldodecyl acetate, (-)-(R)-10-methyl-2-tridecanone, (-)-(R)-(Z)-undec-6-en-2-ol (nostrenol), (-)-(1R, 7R)-1,7-dimethylnonyl propanoate, (-)-(6R, 12R)-6,12-dimethylpentadecan-2-one, (-)-(2S, 11S)-2,11-diacetoxytridecane and (+)-(2S, 12S)-2,12-diacetoxytridecane

Hydrolytic kinetic resolution (HKR) of functionalised epoxides using (salen)Co(OAc) complexes provides enantiomerically enriched epoxides and diols, which have been transformed into important insect sex pheromones. In this general approach, (-)-(R)- and (+)-(S)-10-methyldodecyl acetates from the smaller tea tortrix moth were obtained, as was (-)-(R)-10-methyltridecan-2-one from the southern corn rootworm. The (S)-epoxide obtained from undec-1-en-6-yne was transformed to (-)-(R)-(Z)-undec-6-en-2-ol (Nostrenol) from ant-lions. HKR of appropriate bisepoxides was also investigated, and transformations of the resulting bisepoxides and epoxydiols provided (-)-(1R,7R)-1,7-dimethylnonylpropanoate from corn rootworms, (-)-(6R,12R)-6,12-dimethylpentadecan-2-one from the female banded cucumber beetle, and (-)-(2S,11S)-2,11-diacetoxytridecane and (+)-(2S,12S)-2,12-diacetoxytridecane from female pea-midges

Synthesis and absolute stereochemistry of hagen's-gland lactones in some parasitic wasps (Hymenoptera:Braconidae)

Abstract Efficient syntheses and enantioselective gas chromatography have confirmed the structures and established the absolute stereochemistry of some novel bicyclic lactones (tetrahydrofurofuranones) in species of parasitic wasps (Hymenoptera:Braconidae). The co-occurring γ-lactones, octan-4-olide and dodecan-4-olide, have the ( R )-configuration.