Paul J. Stevenson

The synthesis of fused ring nitrogen heterocycles via regiospecific intramolecular heck reactions

Abstract A series of palladium (and in some cases rhodium) catalysed regiospecific 5-exo-, 6-endo-and 6-exo-trig cyclisations of aryl iodides and vinyl bromides onto proximate alkenes or heteroaromatic rings (indole, pyrrole) lead to a wide variety of fused ring systems. In appropriate cases the methodology provides a facile approach to the creation of tetrasubstituted carbon centres. Double bond isomerisation in the product is only observed in a few cases.

Palladium catalysed tandem cyclisation-anion capture processes. Part 1 : Background and hydride ion capture by alkyl- and π-allyl-palladium species

Abstract A new, wide ranging, synthetically powerful, catalytic tandem cyclisation-anion capture process is proposed which depends on the rate of cyclisation of an organopalladium specifies (RPdX) onto a proximate alkene or diene being significantly faster than anion exchange and reductive elimination in the sequence RPdX → RPdY → RY + Pd(0). The catalytic cyclisation - anion capture sequence is illustrated for hydride capture by a wide variety of substrates giving rise to fused- and spiro-, carbo- and hetero-cyclic systems, regio- and stereo-specifically.

Rhodium catalysed [2+2+2] cycloadditions of acetylenes

Wilkinsons catalyst RhCl(PPh3)3 is an effective catalyst (0.5 – 2 mole %) for the rapid intermolecular trimerisation of 1,6-heptadiynes with monoacetylenes under mild conditions.

Regioselective synthesis of pyrroloquinolines - Approaches to martinelline.

Abstract Indium trichloride catalysed Diels-Alder reaction of imines derived from anilines with cyclic enamides regioselectively gave the biologically important pyrroloquinoline nucleus, with a cis ring junction, in moderate yield. Although the exo:endo selectivity was in most cases poor, these isomers are readily separated by flash chromatography. The functionality tolerated at both C2 and C7 should allow further elaboration to Martinelline

Triterpenoids from Pulsatilla chinensis

A new lupane type triterpenic acid, pulsatillic acid, and two new lupane type triterpenoid glycosides, pulsatilloside A and B, along with the known 23-hydroxybetulinic acid were isolated from the roots of Pulsatilla chinensis. Their structures were characterized as 3-oxo-23-hydroxy-lup-20(29)-en-28-oic acid, 3 beta, 23-dihydroxy-lup-20(29)-en-28-oic acid 3-O-alpha-L-arabinopyranoside and 3 beta, 23-dihydroxy-lup-20(29)-en-28-oic acid 28-O-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside on the basis of hydrolysis and spectral evidence including two-dimensional relay HOHAHA, one-dimensional multiple relay COSY and ROESY NMR techniques. Pulsatillic acid exhibited cytotoxic activities against P-388, Lewis lung carcinoma and human large-cell lung carcinoma.

Regiospecific palladium catalysed tandem cyclisation-anion capture processes. Stereospecific group transfer from organozinc and organoboron reagents

Abstract Vinyl-, alkyl- and π-allyl-palladium species arising from regiospecific palladium catalysed 5- or 6-exo-dig or -trig cyclisations onto proximate alkynes, alkenes or dienes can be intercepted stereospecifically by organozinc or organo boron reagents leading to carbo-and hetero-cyclic compounds in moderate to good yield.

The regioselectivity of rhodium and palladium-catalysed cyclisations of 2-bromo-1,6- and -1,7-dienes

Abstract 2-Bromo-l,6-dienes are catalytically cyclised to a mixture of the corresponding 3,4-bis(methylene)cyclopentane and 5-methylenecyclohex-3-ene. Wilkinsons catalyst shows good selectivity for the 5-membered ring product whilst palladium catalysts, in general, show little selectivity, Addition of tetraethylammonium salts, especially the chloride, allow the palladium catalysed reactions to be carried out at 30°C in good yield and with high selectivity for the 5-membered ring. 2-Bromo-1,7-dienes are cyclised regio-specifically to 6-membered rings by the same catalysts although some double bond isomerisation also occurs. The mechanism of the catalytic cyclisations is discussed. The 3,4-bis(methylene) cyclopentanes undergo facile Diels-Alder reactions.

Regiospecific palladium catalysed tandem cyclisation-anion capture processes. Stereospecific group transfer from organotin reagents.

Abstract Vinyl-, alkyl- and π-allyl-palladium species arising from regiospecific palladium catalysed 5- or 6-exo-trig cyclisations onto proximate alkynes, alkenes or dienes can be intercepted by organotin reagents with stereospecific transfer of an organic group from tin leading to carbo- and hetero-cyclic compounds in moderate to good yield.

Palladium catalysed tandem cyclisation-anion capture processes.Hydride ion capture by alkyl- and π-allyl-palladium species

Abstract Alkyl- and π-allyl-palladium species arising from 5-exo-trig cyclisations onto proximate alkenes or dienes can be intercepted by hydride ion sources leading to carbo- and hetero-cyclic compounds usually in good yield.

Palladium catalysed tandem cyclisation - anion capture processes. Part 2. Cyclisation onto alkynes or allenes with hydride capture☆

Abstract A wide range of palladium catalysed regio- and stereo-specific 5-, 6- and 7-exo-dig mono-, bis- and tris-cyclisation processes of aryl and vinyl halides and allylic acetates are described. The mono- and bis-cyclisation processes terminate in hydride capture from piperidineformic acid or sodium formate. Addition of Tl 2 CO 3 results in alkyne-allene isomerisation and leads, after cyclisation, to 1,3-dienes which give Diels-Alder adducts in good yield.