Ammonia borane as a metal free reductant for ketones and aldehydes: a mechanistic study

Without a catalyst ketones and aldehydes were reacted in THF with ammonia borane (AB) to proceed hydroboration forming alkyl borates. Mechanistic studies revealed that dissociation of ammonia from AB occurred before the hydroboration step. When methanol was used as the solvent, metal free methanolysis of AB would take place with the ketone/aldehyde being directly hydrogenated by the MeOH·BH3 complex.