New approaches to the catalytic activation of arenes and carbonyls

• Main Author: Lomax, Helen
• Other Authors: Williams, Jonathan
• Published: University of Bath 2016
• Subjects: 547
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687388

The activation of styrene towards nucleophilic addition and a Diels‒Alder reaction through η6-binding to ruthenium in [RuCp(η6-stryene)]PF6 has been achieved. Nucleophilic addition solely took place at the terminal carbon of the alkene, to give the anti-Markovnikov product. Good to excellent conversions were gained for a variety of cyclic secondary and primary amines, as well as dimethyl malonate. A Diels‒Alder reaction with 1,2,3,4,5-pentamethylcyclopentadiene was achieved with moderate to good conversions. An SNAr reaction with amines and dimethyl malonate has also been shown to occur with activated 4-chlorotoluene, through [RuCp(η6-4-chlorotoluene)]PF6. Arene exchange has been achieved for [RuCp(η6-benzene)]PF6 with 4-chlorotoluene in up to a 69% conversion using a combination of heat and irradiation using a 400 W medium pressure mercury lamp. Unfortunately attempts to achieve a catalytic reaction proved unsuccessful. The N,N’-dimethylurea promoted activation of 1-chloro-4-nitrobenzene towards SNAr reactions was achieved. Under optimised conditions, good to excellent yields were obtained for a series of cyclic secondary amines. Primary and acyclic secondary amines were less successful under optimised condition, with the exception of 5-amino-1-pentanol. The imidazole catalysed conversion of unactivated carboxylic acids to primary amides was achieved using urea as the nitrogen source. Good to excellent yield were obtained for variety of carboxylic acids under optimised conditions. It was demonstrated secondary amides could also be synthesised, when substituted ureas were used such as N,N’-dimethylurea and 1,3-diphenylurea, to give N-methyl and N-phenyl amides. Although possible mechanisms were explored, results so far are inconclusive.