Radical Cyclizations to Form 1,3-Diols 1)AC O, KF 0%, 3 steps KF, H2O2 85%, 3 steps Note: The rate of 5-exo trig- cyclization radical from 5-exo lization precludes the formation of the 6-er 1)n-Bu3SnH, AIBN R=Ph Nishiyama, H. Kitajima. T: Matsumoto, K ; Itoh, K.J. Org. Chem. 1984, 49, 2298 Transition States Other Examples 1 1)n-Bu3SnH, AIBN 33A-083/149611:36PMPh OH Ph O Si Br Me Me Si O Ph Me Me Ph OAc OH Ph OH OH R O Si Me Me Br R Me OH OH R Me OH OH R OH OH Transition States: O R Si Me Me R1 R2 1) Ac2O, KF 2) H2O2 O Si Me R Me R2 R1 BrCH2SiMe2Cl Me Ph O Si Br Me Me Me O KF, H2O2 Si Br Me Me Note: The rate of 5-exo trig-cyclization is markedly slower when the radical is α to silicon. Thus, 6-endo becomes a competing pathway. In the case of phenyl substitution, the stabilized benzylic radical formed from 5-exo cyclization precludes the formation of the 6-endo product. 1) n-Bu3SnH, AIBN 2) KF, H2O2 80%, 3 steps 85%, 3 steps + Ph n-Bu3SnH AIBN + R = Me R = i-Pr R = t-Bu R = vinyl R = Ph Me Ph 66% 74% 66% 52% 48% 14% - - 9% 4% OH OH 15% 16% 26% 24% 36% Nishiyama, H.; Kitajima, T.; Matsumoto, K.; Itoh, K. J. Org. Chem. 1984, 49, 2298. Me Ph Radical Cyclizations to Form 1,3-Diols: . OH OH . vs. A1,3 strain Me Ph Other Examples: 1) n-Bu3SnH, AIBN 2) KF, H2O2 85%, 2 steps OH OH 1) n-Bu3SnH, AIBN 2) KF, H2O2 94%, 2 steps 1 isomer + 5 : 1 33A-08 3/14/96 11:36 PM