There are disclosed a process for producing an α-acyloxy-α,β-unsaturated carbonyl compound represented by the general formula (VI):
wherein Ri, R 2 and R4 are independently hydrogen atoms or substituted or unsubstituted hydrocarbon residues, or Ri, R 2 and R 4 , when taken together with one another in an optional combination, form a ring, R 3 is a substituted or unsubstituted hydrocarbon residue, and indicates that the configuration may be either E-configuration or Z-configuration, in particular, a 20-acyloxy-17(20)-methylen-21-al-steroid represented by the partial structural formula (II): wherein R is a hydrocarbon residue, and indicates that the configuration of the acyloxy group and the formyl group bonded to the carbon atom at the 20-position may be either E-configuration or Z-configuration, which comprises oxidizing a propargyl ester represented by the general formula (V):
wherein Ri, R 2 , R 3 and R 4 have the same meanings as defined above; an al-steroid compound having the above partial structural formula which is an intermediate for producing a 21-acyloxy-20-keto-delta16-steroid being extremely useful as an intermediate for important corticoids as drugs and obtained by being subjected said al-steroid to isomerization reaction; and a process for producing a 21-acyloxy-20-keto- delta 16 -steroid which comprises oxidation reaction and isomerization reaction.