Alpha-diazocarbonyl-piperidine derivatives : chemoselective rhodium catalysed transformation

Several natural compounds or compounds of biological interest contain the piperidine nucleus that, in many cases, is inserted in complex structures or simply condensed with other rings. Our interest is address to the preparation of different piperidine systems using a very interesting chemistry that combines the use of α-diazocarbonyl compounds and rhodium (II) dimer catalysts. Our studies were focused on the synthesis of piperidine derivatives, or their benzocondensed analogues as well as of more complex structures such as hexahidrobenzophenanthidine alkaloids or crinine derivatives. Several piperidine, all functionalized with diazo-keto function, characterized by a different substitution pattern and stereochemistry, were used as starting materials. These key intermediates when treated with a rhodium catalyst afford electrophilic carbenes that could give a chemoselective C-H or N-H insertion, or reactions with an aromatic ring depending on the nature of the catalyst. Simple diazoketo-piperidine afforded CH insertion giving tropone derivatives. More complex compounds could be obtained from tetrahydroisoquinoline derivatives