Joan Ellison

A novel mass-spectroscopic technique for the investigation of vapour-phase tautomeric equilibria

Comparison of collision-induced dissociation–mass analysed ion kinetic energy (CID–MIKE) spectra of cations found by chemical ionisation ethylation with those of chemical ionisation protonation of fixed ethyl derivatives, allows identification of predominant tautomers in vapour phase equilibria.

1,3-Dipolar character of six-membered aromatic rings. Part 44. Further examples of troponoid synthesis

Adducts formed from 3-hydroxypyridine and two moles of the dipolarophiles, acrylonitrile and methyl acrylate, are converted by quaternisation and Hofmann elimination into 4-cyanotropolone and 4-methoxycarbonyltropolone. Overall yields of ca. 25% are achieved in one-pot reactions from 3-hydroxypyridine 2-Chloro-, 2-bromo-, and 2-cyano-1-methyl-3-oxidopyridinium form adducts with 2π addends, some of which were converted into tropone derivatives.

Pyrylium-mediated transformations of natural products. Part 6. Preparation of pyridinium salts derived from aminoglycosides

Kanamycins A and B react with a variety of water-soluble pyrylium ions in aqueous solution specifically at the 6′-primary-alkyl primary amine functions to give the corresponding pyridinium ions in high yield. Neomycin also reacts at only one amino group. Products were characterised by 13C n.m.r. and elemental analysis.

Kinetics and mechanisms of nucleophilic displacements with heterocycles as leaving groups. Part 8. Conductimetric and spectrophotometric rate constants for the reactions of pyridinium and related cations with piperidine in chlorobenzene

A conductimetric method is developed to obtain rates for the title reactions for which the spectrophotometric method fails. It gives equivalent results. NN′-Dimethylthiourea displaces heterocyclic leaving groups at rates similar to those for piperidine. Compared with α-hydrogen, α-methyl groups render pyridine a less effective leaving group, whereas α-ethoxycarbonyl groups show a large rate enhancement.

The synthesis of some highly strained pyrylium and N-benzylpyridinium salts and kinetics of their reactions with piperidine

5,8-Dimethyl-1-tetralone (11) yields the hindered pyrylium salts (12)—(14), which give the corresponding pyridines and pyridinium salts with ammonia and amines. Chroman-4-one affords the oxoniaphenanthrene perchlorate (17). The additional steric hindrance from the C-methyl groups in (28) and (16) decreases the rate of SN2 displacement. 2,4-Diphenylbenzo[h]chromenylium (7) and 5,6-dihydro-7-phenyldi-benzoxanthylium tetrafluoroborates (8) do not give the corresponding pyridinium salts with aliphatic amines.Benzo[f]chromanone with αβ-unsaturated ketones yielded tetracyclic pyridinium salts (33) and (34). Acenaphthenone derived pyrylium salts (39), (40), and (46), were prepared from benzylideneacetophenone, styryl t-butyl ketone, and benzo[f]chromanone. Kinetic measurements on derived N-benzylpyridinium salts demonstrated that the αβ-fusion of an acenaphthene ring decreased the tendency of a pyridine to act as a leaving group compared to the corresponding 2-phenylpyridine.