Development of new methodology for the synthesis of fluorine-containing compounds
A set of mild conditions for the pentafluorophenylation of carbonyl compounds employing copper-bisphosphine catalysis have been developed. The optimised conditions allow access to a wide range of pentafluorophenyl benzyl alcohols in high yields. The reaction of aliphatic aldehydes and particularly electrophilic ketones to give products in moderate yields is also disclosed. An investigation into the reactivity of β-fluoroalkyl-α ,β -unsaturated carbonyl compounds was conducted. Asymmetric copper hydride reduction of β -fluoroalkyl-α , β-unsaturated ketones was found to preferentially give the allylic alcohol product resulting from 1,2 attack in up to 62% ee. Reaction of β-fluoroalkyl-α , β-unsaturated esters under similar conditions gave the product of conjugate reduction in higher enantiomeric excess; up to 99% was observed. Rhodium-catalysed arylation of β -fluoroalkyl-α , β-unsaturated ketones was also found to give the product of direct carbonyl attack. Conditions for the racemic reaction are described along with those for the enantioselective reaction of methyl ketones in up to 74% ee. Ruthenium catalysed arylation of β-fluoroalkyl-α ,β -unsaturated aldehydes employing Me-Bipam as ligand gave the desired secondary allylic alcohols in good yields and good to excellent enantiomeric excesses (14 examples, 76-87% ee).