SIA heterocycles possessing different ring sizes were also explored. The 9-membered SIA when reacted with E2 was highly enantioselective, 27 (99:1 e.r.), compared to the 6membered SIA, 30 (91:9 e.r.). The enantioselectivity resulting from the reaction of E4 with either the 9-membered or the 6membered SIA was significantly diminished compared to analogues product 5. Surprisingly, the 5-membered SIA heterocycle was found to decompose under the reaction conditions and no desired product was observed. These results indicate that ring size has a significant effect on enantioselectivity, with 7-membered SIAs seemingly representing the ideal ring size for the highest enantioselectivity with either electrophile. Our results are consistent with the prototypical catalytic cycle for palladium-catalyzed alkylation reactions. The ionization event releases CO2 and t-butoxide that is essential in the desymmetrization reaction (Figure ). The liberated tbutoxide deprotonates the SIA, and generates a prochiral anion nucleophile which can then react with the chiral -allyl complex through the transition state model proposed by Trost. The steric profile of L1 influences which enantiotopic nitrogen of the SIA attacks the π-allyl complex. The absolute stereochemistry observed in crystal structures 12 and 21 results from the enantiotopic nitrogen atom highlighted in blue reacting with the π-allyl complex (Figure ). In the disfavored conformation the p-tolyl group clashes with the wall of the catalyst pocket and the R group of the 2-substituted allyl. A vertical flip of the SIA results in the favored nucleophilic approach. In the favored conformation the p-tolyl group is positioned in the flap portion of the catalyst pocket and the cyclic portion of the SIA is pointed down and away from R group of the allyl complex, minimizing the steric clash of the chiral π-allyl and the nucleophile. The effect of R on enantioselectivity is apparent as larger R substitution leads to higher enantioselectivity in general. Overall, the enantioselectivity of the desymmetrization reaction is determined by the minimization of steric clash between the nucleophile and L1.