α-Formylations with Chiral Chloroiminium Salts
The synthesis of quaternary carbon centres is a challenging task in organic chemistry, and this is believed to be due to the significant amount of ‘steric crowding’ involved in the creation of a quaternary carbon centre. This thesis discusses the discovery and development of a new method for the preparation of α-formyl ketones containing an α-quaternary carbon centre. Ketone substrates were reacted with the Vilsmeier reagent (chloromethylene) dimethylammnonium chloride (generated in situ from DMF and oxalyl choride) followed by work up with aqueous base (NaHCO3) to afford α-formyl ketones (8-88% yield). This methodology was extended to the asymmetric α-formylation of α-methyl indanone and α-methyl tetralone using chiral chloroiminium salts derived from (S)-proline. The asymmetric reactions gave enantiomeric excesses of up to 68%.
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