CARBONYLATIVE COUPLING OF ORGANOZINC REAGENTS IN THE PRESENCE AND ABSENCE OF ARYL IODIDES - SYNTHESIS OF UNSYMMETRICAL AND SYMMETRICAL KETONES

The utility of the palladiun(O) catalysed reaction of the iodoalanine- derived organozinc reagent 6a with functionalised aryl iodides, under a carbon monoxide atmosphere, to give protected 4-aryl-4-oxo alpha-ami no acids 8, is illustrated by a short synthesis of L-kynurenine 4. Tre atment of functionalised organozinc reagents with catalytic tetrakis(t riphenylphosphine)palladium(O) under an atmosphere of carbon monoxide, in the absence of any electrophile leads to the formation of symmetri cal functionalised ketones 9 in good yields, This reaction is illustra ted by a one-step synthesis of protected (2S,6S)-4-oxo-2,6-diaminopime lic acid 9a from commercially available compounds, It has been establi shed that adventitious molecular oxygen plays a key role in the format ion of the symmetrical ketones 9, and that rigorous exclusion of oxyge n can result in substantially higher yields of ketones 8 in the cross- coupling with some aromatic iodides.