Stepwise hydroformylation of C,N-divinylpyrroles with Rh4(CO)12 under mild conditions: an original synthesis of N-vinylpyrrolylmonoaldehydes and of pyrrolyldialdehydes

1,3-Divinylpyrrole and 1,2-divinylpyrrole were treated in a stainless steel autoclave with Rh4(CO)12 at 40°C and 120 atm of H2/CO total pressure: for both substrates exclusive hydroformylation of the vinyl groups bonded to the ring carbon atom occurred, the branched unsaturated monoaldehydes 2-(1-vinylpyrrolyl)propanals being formed with a very high chemoselectivity and α-regioselectivity. At 80°C only 1,3-divinylpyrrole gives, via hydroformylation of N-vinyl group, the corresponding dialdehydes.