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X . WA N G , Y. L U , H . - X . D A I , J . - Q . YU * ( T H E S C R I P P S R E S E A R C H I N S T I T U T E , L A J O L L A , USA) Synthesis of Heterocycles Pd(II)-Catalyzed Hydroxyl-Directed C–H Activation/C–O Cyclization: Expedient Construction of Dihydrobenzofurans J. Am. Chem. Soc. 2010, 132, 12203-12205. K e y w ord s Palladium(II)-Catalyzed Heteroannulation Route to Dihydrobenzofurans 3 Pd(OAc)2 (5 mol%) PhI(OAc)2 (1.5 equiv) R R1 H OH Li2CO3, C6F6, 100 °C, 36 h 1 dihydrobenzofurans C–H activation palladium 4 5 R1 6 R2 O R3 This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. R2 C a te go r y 2 42–91% yield 22 examples R1 = H, 4-Me, 5-Me, 6-Me, 5-OMe, 6-OMe, 6-F, 4-Cl, 5-Cl, 6-Cl, 4-Br, 6-Br, 6-CF3, 6-CO2Me, 5,6-(OMe)2 R2 = Me, Et, n-Pr R3 = H, Me, n-Pr, i-Bu, Bn, Ph, CO2Et Significance: Reported is the synthesis of di- hydrobenzofurans 2 from homobenzylic alcohols 1 via an intramolecular palladium-catalyzed C–H activation/C–O cyclization sequence. Both EDGs and EWGs are tolerated at various positions around the ring. Yields are excellent (>75%) in almost all cases, except for R3 = CO2Et (50%) and R3 = H (42%). The stability of halogen substituents (R1 = Cl, Br) to the reaction conditions, providing a handle for further functionalization, is worthy of note. Two examples of spirocyclic dihydrobenzofurans (a model system for the core structure of the natural product stachybotrylactam) were also prepared in high yield. Comment: The dihydrobenzofuran ring system is common in many natural products (e.g. stachybotrylactam, rocaglamide) and pharmaceuticals (e.g. oxycontin). Although amine-directed C–H activation for the formation of azacycles has been previously developed, the use of a hydroxyl group for such a process is less common. The current method provides a convenient entry into dihydrobenzofurans in excellent yield and with high functional group tolerance. The scope of this methodology is limited, however, by the need for a 2,2-dialkyl moiety to achieve the best yields. Victor Snieckus, Timothy Hurst Synfacts 2010, 11, 1223-1223 Publishedonli e:x .x .201 Published online: 21.10.2010 DOI: 10.1055/s-0030-1258837; Reg-No.: V13310SF © Georg Thieme Verlag Stuttgart · New York SYNFACTS Contributors: 2010 © THIEME STUTTGART • NEW YORK 1223