 <unk> trapping with various electrophiles is decidedly less common . In one study , the <unk> <unk> is paired with a Michael reaction using an iridium catalyst to initiate nucleophilic conjugate addition of the <unk> to β @-@ <unk> . In this tandem reaction the iridium catalyst is required for both conversions : it acts as the Lewis acid in the <unk> <unk> and in the next step the nitro group of <unk> first coordinates to iridium in a ligand exchange with the carbonyl ester oxygen atom before the actual Michael addition takes place to the opposite face of the R @-@ group . 
