Palladium-Catalyzed Cross-Coupling of Terminal Alkynes with 4-Trifloyloxazole: Studies toward the Construction of the C26−C31 Subunit of Phorboxazole A
摘要:
[GRAPHICS]A strategy has been developed that successfully takes advantage of transition-metal-catalyzed coupling reactions for the synthesis of highly functionalized oxazoles. Trifloyloxazoles have been used as coupling partners with alkyne-derived vinylmetallic intermediates in Stille- and Negishi-type couplings to assemble the corresponding oxazoles in good isolated yield. The results obtained provide a close analogy and thus good precedent to employ this strategy in the synthesis of the oxazole subunits of phorboxazole A.
Rhodium complexes (RhClL3, RhCl(CO)L2, [RhCl(COD)]2; L=PPh3) catalyze hydrostannation of terminal acetylenes (RC≡CH; R=Ph, Me3Si, R1OC(R2)(R3), and R1OCH2CH2; R1=THP, OAc; R1, R2=H, Me) with Bu3SnH to produce R(Bu3Sn)C=CH2 selectively. Other transition metal complexes [MCl2L2(M=Ni, Pd, Pt, Co)] are also active for the hydrostannation, but with less selectivity.