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. Author manuscript; available in PMC: 2008 Aug 6.
Published in final edited form as: Nat Prod Rep. 2008 Apr 14;25(4):719–737. doi: 10.1039/b706296f

Scheme 22.

Scheme 22

Schreiber’s branching pathway using boronic esters. Reagents and conditions: (1) 78 (3 eq.), Grubbs’ 2nd-gen. cat. (20 mol%), CH2Cl2, reflux, then H2O; yield range: 78-92%; (2) H2O2, NaOH, THF, rt, 56% (over 2 steps) [R1 = CH2OTIPS; R2 = Me]; (3) OsO4, NMO, acetone, pH 7 buffer; then 2,2-dimethoxypropane, CH2Cl2, PPTs; then H2O2, NaOH, THF, 66% (over 2 steps) [R1 = CH2OTIPS; R2 = Me]; (4) N-benzylmaleimide (8 eq.), PhMe, 80 °C; then H2O2, NaOH, THF; carried out on solid support [typical yields for the Diels–Alder reaction of related substrates in solution: 81-91%].