D A Evans, J. Johnson Rules for Ring Closure: SP2 Carbon& Related Systems Chem 206 Trigonal Carbon: EXocyclic Enolate Alkylation distance between reacting exo By definition, an exo-tet cyclization, but stereoelectronically behaves as an endo trig he overlap for C-alkylation is poor due to geometrical constraints of 5-membered ring only observed product distance between reacting The relaxed geometrical constraint KOt-Bu or LDA provided by the added CH2 group >95% by nMr now renders the 6-membered Baldwin. J. chem. Soc. Chem. Commun. 1977. 233 === a Given the failure of the enolate alkylation shown above(eq 1), explain why these two cyclizations are successful base Favorskii Rearrangement (Carey, Pt B, pp 609-610 Your thoughts on the mechani base NH OMs Meo Mec-D. A. Evans, J. Johnson Rules for Ring Closure: SP2 Carbon & Related Systems Chem 206 Trigonal Carbon: Exocyclic Enolate Alkylation Br MO Me Me Me Br Me Me O O Me Me ■ By definition, an exo-tet cyclization, but stereoelectronically behaves as an endo trig. KOt-Bu or LDA > 95% by NMR O Me Me O Me Me X Y C Y - exo C C C C O C –O only observed product However: Baldwin, J. Chem. Soc., Chem. Commun. 1977, 233. N O R R Ar R OMs R O NH Ar base N O Ar base NHAr O Br ■ Given the failure of the enolate alkylation shown above (eq 1), explain why these two cyclizations are successful. (1) Br MO O X The overlap for C-alkylation is poor due to geometrical constraints of 5-membered ring distance between reacting centers: 3.04Å distance between reacting centers: 3.37Å MO Br O The relaxed geometrical constraint provided by the added CH2 group now renders the 6-membered cyclization possible Favorskii Rearrangement (Carey, Pt B, pp 609-610) Your thoughts on the mechanism Cl O MeO– O CO2Me MeO– –HCl