Alan J. Whittle

Total synthesis of the insect antifeedant ajugarin I and degradation studies of related clerodane diterpenes

Abstract The first total synthesis of the diterpene clerodane insect antifeedant ajugarin I (1) has been achieved. The key step of the synthesis discloses the use of the 1,3-dithiolane unit to stereochemically direct the conjugate addition of a but-3-enyl cuprate to set in place the C-10 sp3 carbon centre. The trans -fused ring geometry was obtained by conjugate additon of a vinyl cuprate to an enone and regio and stereoselectively trapping the resulting enolate with formaldehyde. Introduction of the necessary butenolide side chain was achieved by conjugate addition of a sulphone stabilised anion to ethyl-4-(t-butyldimethylsilyloxy) but-Z-ynoate followed by work-up with fluoride. Final hydroxyl directed epoxidation was not specific giving both the natural product ajugarin I and its 4-epi isomer. Chemical modification of the insect antifeedant clerodin hemiacetal afforded a series of side chain modified structures for biological evaluation.

Efficient aromatic and heteroatom acylations using catalytic indium complexes with lithium perchlorate

The combination of an indium complex with lithium perchlorate affords a potent system for the catalytic acylation of electron-rich aromatics and alcohols. The use of isopropenyl acetate as acyl donor results in cleaner methodology with acetone as the only by-product. The study has also revealed an indium-catalysed ketalisation reaction.

A convenient preparation of 2-haloenones from enones using phenylselenium halides

Abstract Enones can be converted in high yield to their corresponding 2-halo analogues by treatment with an excess of phenylselenium halide in methylene chloride/pyridine at 37°C.

Selenium-mediated cyclization reactions of alkenyl-substituted β-ketoesters

Phenylselenating agents, in which the counter ion is non-nucleophilic, react with certain alkenyl-substituted β-ketoesters to afford cyclized products, some of which can be further rearranged using SnCl4.

An enantiospecific total synthesis of allosamizoline

Abstract An enantiospecific total synthesis of allosamizoline has been accomplished in a short stereoselective sequence starting from glucosamine.

The total synthesis of the clerodane diterpene insect antifeedant ajugarin I

The first total synthesis of the polyoxygenated diterpene insect antifeedant ajugarin I (1) has been achieved by a route which involves a new method for the construction of 3-substituted-Δ2-butenolides.

Synthesis of a trans-decalin as a potential insect antifeedant

In a model study for the synthesis of clerodane-related insect antifeedants the trans-decalin (3) was prepared and shown to inhibit feeding of Locusta migratoria.

Synthesis of polyoxygenated trans-decalins as potential insect antifeedants

2α, Acetoxy-1α-acetoxymethyl-5,5-dimethyl-1α,6β,10Oα-bicyclo[4.4.0]decane-10-spiro-2′-oxiran (4) has been prepared from 4,4-dimethylcyclohex-2-enone as a model compound in order both to probe the biological activity of, and to develop a synthetic strategy to, a number of clerodane-related insect antifeedants. The trans-decalin (4) was shown to inhibit feeding of Locusta migratoria at a comparable level to that of the natural product clerodin hemiacetal. Three other related decalin analogues were also synthesised and shown to have negligible antifeedant properties.