NITRILIMINES - EVIDENCE FOR THE ALLENIC STRUCTURE IN SOLUTION, EXPERIMENTAL AND AB-INITIO STUDIES OF THE BARRIER TO RACEMIZATION, AND FIRSTDIASTEREOSELECTIVE [3-CYCLOADDITION(2])

The lithium salts of s(diisopropylamino)thioxophosphoranyl]diazomethan e (2) and (dicyclohexylamino)thioxophosphoranyl]diazomethane diazometh ane (5) react with the iisopropylamino)(dicyclohexylamino)chlorophosph ine (3) and bis(diisopropylamino)chlorophosphine (6), leading to the n itrilimines 4 (63% yield) and 7 (69% yield), respectively. The lithium salt of 2 also reacts with the bis(dicyclohexylamino)phosphenium ion, affording nitrilimine 9 in 51% yield. Using the presence of a chiral substituent either at the carbon or at the nitrogen terminus of the CN N skeleton, variable-temperature solution NMR studies of nitrilimines 4 and 7 demonstrate that they possess a bent allenic structure. The fr ee energy of activation for racemization is ca. 30 kJ mol(-1). Ab init io/DFT studies performed on nitrilimine with C-P(S)H-2 and N-PH2 subst ituents 10 show that the most likely pathway for the racemization proc ess is inversion at the carbon atom, followed by rotation of the PSR(2 ) fragment. Bis(trityl)nitrilimine 17 reacts with (acryloxy)-beta,beta -dimethyl-gamma-butyrolactone, leading to diastereomeric pyrazolines 1 8a,b (3/1 ratio) in 60% total yield; this is the first example of a di astereoselective [3 + 2]-cycloaddition reaction involving a nitrilimin e.