In the original work, Cornforth used 5-ethoxy-2-phenyloxazole-4-carboxamide (R = phenyl, R = ethoxy, R = amino).
The reaction also works, however, with a large number of other carbonyl-substituted 1,3-oxazoles.
In the early 1970s, the reaction was further researched by Michael Dewar. It was shown that the reaction gave good yields, over 90%, when using nitrogen-containing heterocycles at the R position.