Carbonyl Groups as Substituents

The second large class of allenes with carbonyl groups as substituents is derivatives of carboxylic acids. Overall, the same principles as with the aldehydes and ketones apply, but not as many examples are known, which might originate in part from the lower acidity of the a-hydrogen atoms of the carbonyl group compared with aldehydes and ketones. 

COPh. In general, it appears that carbonyl groups as substituent are better endo directors than cyano, but the situation is sometimes complicated by subsequent endo/exo equilibration of the adducts. 

---