David A. H. Taylor

Tetranortriterpenoids and related compounds. Part 22. New apotirucailol derivatives and tetranortriterpenoids from the wood and seeds of chisocheton paniculatus(meliaceae)

Five new compounds, the apo-tirucallol derivatives (1), (9), (13), and (16) and the tetranortriterpenoid vilasinin 1,3-diacetate (18), have been isolated from the wood of Chisocheton paniculatus(Meliaceae). From the seeds of the same tree four new tetranortriterpenoids have been obtained, including the γ-lactone (22), the hemiacetal (23), the γ-hydroxybutenolide (24), and 17β-hydroxy-6α-acetoxynimbinin (26). Compounds (22) and (23) are possible precursors of normal furanoid tetranortriterpenoids. 13C and 1H n.m.r. Data for these nine compounds are reported.

Novel annulation reactions: A simple preparation of spirocycles and an allylsilane based bifunctional acceptor-donor annulating reagent

Abstract A simple, one pot, stereoconvergent synthesis of spirocycles has been achieved in excellent yield. Further studies on one step bifunctional annulating reagents have resulted in the development of a new allylsilane based cyolopentannulation reaction.

The preparation and reactions with an o-silylated enolate of an allylsilane bifunctional [3 + 2] annulating reagent

Abstract The preparation and reactions of allylsilance-acetal (13) with various silyl enol ethers are described. This results in the one-pot synthesis of fused and spiro cyclopentanes by using a 1,3-bifunctional annulating reagent in which the two reactive centres are activated by one set of conditions .

Ellipsometric studies of ferrocene-containing copolymer films: Part 1. Data analysis strategy for deposition and voltammetric characterisation experiments

Abstract Ellipsometry has been used to study the deposition and properties of 35:65 poly(vinylferrocene-co-vinylpyrrolidone). Deposition on Pt was carried out by electrochemical oxidation of neutral polymer in CH 2 Cl 2 solution. Comparison of coulometric and ellipsometric data shows that, initially, all the oxidised ferrocene becomes surface immobilised. Subsequently, only a small (decreasing) fraction of the material oxidised becomes attached to the surface. Voltammetric experiments were carried out after transfer of the oxidised films to aqueous medium. A linear variation of the product kL (where k is the complex component of the film refractive index, and L is the film thickness) with charge was found. From this relationship, optical constants for the fully oxidised and fully reduced films were obtained. The parameters obtained differ from those for monomeric species in solution as a result of incorporation in the surface attached polymer film.

A synthesis of methyl 2α-acetoxy-3-deoxo-3α-hydroxyangolensate

The title compound (1a) has been partially synthesised from gedunin. It is the first natural 1α, 2α, 3α-trihydroxy terpene molecule to have been synthesised. Attempts to introduce a 2α-hydroxy group into a preformed methyl angolensate derivative failed, and the synthesis was achieved by the prior preparation of 2α-acetoxy-7-deacetoxy-7-oxokhivorin (2a), 1 which was converted into the title compound. The key stage in the conversion is the Baeyer–Villiger oxidation of the 7-oxo group to a lactone, which was studied in some detail. The use of buffered peracetic acid effects the required oxidation in good yield without oxidising the furan ring; the use of pertrifluoroacetic acid oxidises the furan ring to an unsaturated lactone without attacking the carbonyl group. The implications of this are considered in an Appendix.

The synthesis of a 1α,2α,3α-triacetoxy limonoid

The report1 that Meerwein–Ponndorf reduction of gedunin (1a) gives 3α-hydroxy-3-deoxogedunin (2a) is wrong; the product is the 3β-epimer (2b). 3α-Acetoxy-7-deacetoxy-3-deoxo-7-oxogedunin (3c) was prepared by a stereospecific synthesis from cedrolide (1b), 7-deacetoxy-7-oxogedunin; osmium tetroxide oxidation then gave the 1,2α-glycol, isolated as the acetate (4a). Similarly, oxidation of the 3β-alcohol (3b) also gave the α-oriented glycol, as anticipated from the steric hindrance of the β-face of the molecule.Oxidation of the allylic alcohols (2b) or (3b), or of the allylic acetate (2d) with perbenzoic acid also takes place from the α-face of the molecule, giving the corresponding α-oxides (5a–c). The oxidation is pH sensitive; with a benzoate buffer the 7-oxo group in alcohol (3b) undergoes Baeyer–Villiger oxidation, giving the Iµ-lactone isolated as the acetate (6a). Opening of the oxide ring in the 3β,7α-diacetoxy oxide (5c) is complex. Identification of the products shows that the reaction involves participation by both the acetate groups. In contrast the 3β-acetoxy-7-oxo compound (5d) and the Iµ-lactone (6a) give the products of ring opening with assistance from the neighbouring acetate group, while the 3β-hydroxy compound (5b) gives the simple bromohydrin.

2β-Alkyl derivatives of gibberellin A1

In the reaction of gibberellin A3(1) with lithium dialkylcuprates, anti-SN2′-type substitution occurred with the displacement of the lactone function. The resultant 2β-alkyl-1(10)-enedioic acids (4)–(7) were iodolactonised, then reductively de-iodinated to give 2β-methyl, 2β-ethyl, 2β-n-propyl, and 2β-n-butyl gibberellin A1(16)–(19). The reaction of lithium dimethylcuprate with 3-didehydrogibberellin A3 was complex but there was no evidence for the occurrence of conjugate addition to the α,β-unsaturated ketone in competition with the anti-SN2′-type reaction.

Limonoid extractives from species of Guarea. An unusual shielding effect on an acetyl group

The bark of Guarea species has been found to be a rich source of limonoids. One has been identified as methyl 6,12α-diacetoxyangolensate (1; R = OAc); the 12-acetyl group in this is strongly shielded by the furan ring.

Vilsmeier formylation of tert-anilines: dibenzo[b,f][1,5]diazocines and quinazolinium salts via the ‘t-amino effect’1

The attempted Vilsmeier ortho-formylation of p-substituted N,N-dimethylanilines 1 with N-formyl-N-alkylarylamides 2 unexpectedly gives dibenzo[b,f][1,5]diazocines 5 in 26–74% yield. This reaction proceeds by Vilsmeier formylation ortho to the dimethylamino group of 1 followed by hydride migration from the N-methyl group to the newly formed iminium CH group, followed by intramolecular cyclisation, a new example of the ‘t-amino effect’. Similar formylation of cyclic tert-anilines such as 4-tolyl-pyrrolidines 6a,e,g, -piperidines 6b,f,h, -perhydroazepines 6c,i and -morpholine 6d, however, shows a different chemistry giving diformylated enamines 7 as the major products (12–60%). A small amount of diazocines 8 (1–13%) with a substituted benzyl at the nitrogen and N-formylated diazocines 9 are also isolated in some cases. When N-formyl-1,2,3,4-tetrahydroquinoline is used as the Vilsmeier reagent, normal formylation is observed, while use of aliphatic Vilsmeier reagents such as DMF and N-formylmorpholine give quinazolinium salts 16 and 17, also by way of the ‘t-amino effect’. The key feature in these formylations is the hydride transfer from the α-position of a tertiary amine to an unsaturated ortho-substituent CHNR2+, the ‘t-amino effect’.