Ketene chemistry computations

Let s start with what looks like a simple problem what can computational chemistry tell us about oxirene (oxacyclopropene, Fig. 9.1 the oxirene literature till 1983 has been reviewed [2]). Labelling one of the carbons of a diazo ketone (R-C(N2)-CO-R) can lead to a ketene with scrambled labelling. After excluding the possibility of scrambling in the diazo compound, this indicates that an oxirene... 

The transient decays at the same rate that cyclic keten-imine 51 is formed, suggesting that the newly detected transient is singlet phenylnitrene ( 49). This assignment was secured with the aid of computational chemistry i and by studying the temperature dependence of the kinetics. 

Subbotina and co-workers recently studied the synthetic and theoretical aspects of the generation of 6-hydroxypyridin-2-ones from the corresponding 6-aminopyran-2-ones. Treatment of 104 or 106 with pyridine in DMF at 120 °C gave the corresponding Dimroth products 105 and 107 in 70% and 57% yield, respectively. The authors used computational chemistry to rationalize the generation of a nonisolatable ketene intermediate in the reaction. 

---