Scheme 27. Spring's branching pathways strategy using the fluorous-tagged diazoacetate 110. Reagents and conditions: (1) C6H6, Rh2(O2CCF3)4, 70%; (2) dimethyl acetylenedicarboxylate [DMAD], 84% (88%); (3) PhCHO, PhNH2, then DMAD, Rh2(OAc)4, d.r. 95 : 5, 51% (80%); (4) LDA, R1COR2, then Rh2(OAc)4; 111d: 49% (90%); 111e: 68% (97%); (5) DMAD, 59%; (6) MeNH2, NaOH, then MeOH, H2SO4, 35%; (7) resorcinol, H2SO4, 74% (95%); (8) thiophene-2-carboxaldehyde, guanidine carbonate, then 3-formylchromone, 43% (98%). RF = C6F13CH2CH2–. Numbers in parentheses are purities determined by HPLC, LC-MS or 1H NMR spectroscopy.
