Philip J. Parsons

Tandem radical cyclisations : Synthesis of lysergic acid derivatives

Abstract A novel free radical cyclisation approach for the synthesis of lysergic acid analogues has been investigated. The homolytic cleavage of carbon-bromine bond, mediated by tri-n-butyltin hydride, led to the development of a method for the construction of 3,4-disubstituted dihydroindoles via single cyclisation; hexahydrobenz[cd]indoles via double tandem cyclisations and both octahydroindolo[6,5,4-cd]indoles and decahydroindolo[4,3-fg]quinolines via triple radical cyclisations. A successful tandem double 5-exo-trig,6-endo-trig cyclisation of aryl radical generated from N-3-[3-(N-acetyl-N-allylamino)-2-bromophenyl]-5-(carbomethoxy)-1,4,5,6-tetrahydro-N-methylpyridine afforded methyl 1-acetyl-2,3,9,10-tetrahydrolysergate.

1,5 Allylic abstraction, cyclisation: A new route to five membered carbocycles

Abstract A new 1,5 allylic abstraction cyclisation sequence has been developed. The method is based upon a novel radical rearrangement and is applicable to the construction of highly functionalised cyclopentanoid ring systems.

The facile construction of indole alkaloid models: A tandem cascade approach for the synthesis of a model for pseudocopsinine

Abstract A short and concise route to the pseudocopsinine skeleton is reported which relies on a tandem radical cascade to furnish five fused rings in one step.

A free radical approach to cyclopentanone and spirocyclic systems: Development of a 1,5 allylic abstraction-cyclisation sequence

Abstract A novel free radical approach to cyclopentanone and spirocyclic ring systems is described. This work illustrates the potential of the 1, 5 allylic abstraction-cyclisation reaction and demonstrates the application of the sequence to systems in which alternative radical cyclisation pathway can be envisaged.

Approaches to bicyclic ring systems via 1,5 allylic abstraction cyclisation

Abstract A new 1, 5 allylic abstraction, cyclisation sequence has been developed and applied to the synthesis of fused bicyclic systems. Initial studies directed towards the synthesis of the bicyclo[3.3.0] octane skeleton are described: vinyl bromide 4 was subjected to standard cyclisation conditions to give 5 as a single isomer. Further studies were directly related to the development of the rearrangement sequence: vinyl bromide 10 was subjected to cyclisation conditions to give 12 in moderate yield. A significant improvement in the rate and efficiency of this type of conversion was achieved by introducing an electron withdrawing group on the acceptor alkene, thus compound 17 gives 18 in excellent yield.

A synthesis of the hexahydrobenzofuran portion of the avermectins I. Model studies

Abstract A tandem radical cyclisation has been used to construct a model for the synthesis of the hexahydrobenzofuran moiety present in the avermectins.

Convenient synthesis of allenyl sulphides; application to the synthesis of αβ-unsaturated ketones

P2S5 in methylene chloride containing pyridine reduces allenyl phenyl sulphoxides to sulphides; the difficult hydrolysis of the latter is eased by the introduction of a methoxy group into the benzene ring and this method then becomes a practicable synthesis of αβ-unsaturated ketones.

2-Phenylthioallyl alcohols and their use in the synthesis of 1,4-diketones and cyclopentenones

1-Phenylthiovinyl-lithium adds to n-hexanal to give the allylic alcohol (II) that undergoes the Carroll and Claisen rearrangement with formation of the carbonyl compounds (IV) which can be converted into dihydrojasmone (VIa) and 2-n-pentylcyclopent-2-enone (VIb) by hydrolysis and cyclisation.

The Generation of Double Bonds of Specific Geometry by Regioselective Addition of Organotin Cuprates to Propargylic Ethers

Abstract A new synthesis of rings is described which relies on addition of Lipshutz reagent to an acetylene followed by intramolecular trapping of the resulting cuprate with electron deficient double bonds.

A novel synthetic approach to the cardiotoxin Batrachotoxin: An efficient synthesis of the AB ring system

Abstract A chiral synthesis of the AB ring system of Batrachotoxin (1) is reported. The synthesis utilises a carbene mediated ring expansion of a chiral hydrindane.