Please explain. An abbreviated mechanistic description for DCC-mediated amide bo
ID: 1060216 • Letter: P
Question
Please explain.
An abbreviated mechanistic description for DCC-mediated amide bond formation is illustrated as Path A. An alternative pathway for this process has been proposed as well, illustrated in Path B. In this alternative pathway, a second molecule of add 1 out-competes the amine 4 for the pivotal activated acyl derivative 3, leading to a transient symmetrical anhydride 7 (with discharge of 6). In Path B, anhydride 7 then is the active electrophile that reacts with amine 4 to give the observed amide product 5 with regeneration of one molecule of acid 1. Assuming that only Path B were operational, what amide product(s) would you anticipate if the reaction were run with 1 equiv. of the achiral acid 8, 1 equiv. of the racemic amine 9, and a limiting amount (0.1 equiv.) of the chiral dimide 10? Select one: Chiral amide 11a only. Chiral amide 11b only. An equal mix of 11 a and 11 b (= racemic mix). An unequal mix of 11a and 11b.Explanation / Answer
Since the acid is achiral and only path B is operational the active species will be achiral anhydride 7. This anhydride can react with both the enantiomers of amine with the same rate. So, there will not be any effect of chirality of diimide on selectivity and an equal mixture of 11a and 11b (= racemic mixture) will be ontained.