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1.2.3.5.2 Tandem Michael Addition Followed by Intramolecular Addition of Malonate Derivatives to Alkynes

DOI: 10.1055/sos-SD-001-00206

Takacs, J. M.; Vayalakkada, S.; Jiang, X.Science of Synthesis, (20011301.

A novel one-pot procedure for the preparation of highly functionalized 3-methylenetetrahydrofurans 151 has been formulated that exploits the intramolecular palladium-catalyzed addition of malonate anions to an alkyne (Scheme 41).[‌37‌] The methodology is based on the base-catalyzed Michael addition of propargyl alcohols to alkylidene- or benzylidenemalonates (i.e., 149). This addition presumably affords an intermediate such as 150 which subsequently undergoes a palladium-mediated exo-dig cyclization. Various bases (e.g., NaH, t-BuOK, BuLi) and various palladium complexes {[Pd(OAc)2(PPh3)n] (n=1 or 2), Pd(PPh3)4, [Pd(dba)2(PPh3)]} have been successfully used in the reactions. It is notable that either palladium(0) or palladium(II) complexes afford active catalysts for this variant. The best result is obtained when catalytic [Pd(OAc)2(PPh3)] is used as the catalyst precursor and catalytic butyllithium is used to generate the alkoxide from the propargyl alcohol; good results are obtained with a variety of alkylidene derivatives.

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