Evans. Breit Electrocyclic Processes-3: 3-Atom Electrocyclization Chem 206 Three-Atom Electrocyclization (2 electrons Solvolysis of Cyclopropyl Derivatives Does solvolysis proceed via cation 1 followed by rearrangement to 2 ( Case 1), or does it proceed directly to 2( Case 2)? Con?? fast Case 2 nonbonding Me tso 000 cation relative rate 40,000 LUMO DePuy, Accts. Chem. Res. 1967, 1, 33 X LUMO HOMO Note that there are two disrotatory modes HOMO RDis LUMO X Sterically favored Favored for R=ring HOMO+ + Y3 Y1 Y2 A H R H A R A H A H R C A H H A X R R R R X R R LUMO C C R A H H A A A R H H R R HOMO LUMO LUMO X X H TsO X C C R H Me Me H C C R Me H H Me X HOMO HOMO –X– –X– H TsO Me Me H H H +X– R Me H H Me H TsO H H Me Me R H Me Me H X +X– Electrocyclic Processes-3: 3-Atom Electrocyclizations Chem 206 Sterically favored Dis Favored for R = ring Dis Three-Atom Electrocyclizations (2 electrons) Dis?? Con?? Dis Note that there are two disrotatory modes Dis + + Evans, Breit nonbonding cation anion Solvolysis of Cyclopropyl Derivatives slow fast slow Does solvolysis proceed via cation 1 followed by rearrangement to 2 (Case 1), or does it proceed directly to 2 (Case 2)? 1 2 2 Case 2 Case 1 relative rate 1 4 40,000 Dis DePuy, Accts. Chem. Res. 1967, 1, 33 fast fast