Rhodium-catalyzed deuterioformylation of the ketal-masked β-isophorone: Evidence for a tertiary alkyl rhodium intermediate as a precursor of the main reaction product acetaldehyde derivative

The rhodium-catalyzed deuterioformylation of the ketal-masked β-isophorone 7,9,9-trimethyl-1,4-dioxa-spiro[4.5]dec-7-ene (1) under 100 atm of syngas, at 100 °C, gives the trideuterated acetaldehyde derivative 2 as the main product, originating from a primary alkyl rhodium intermediate c via isomerization of the tertiary one a. Theoretical calculations indicate that secondary and tertiary rhodium alkyl intermediates are formed in a similar amount and hence their evolution to aldehydes occurs with different rates.