Palladium-Catalysed Alkynylations of 2-Pyrone (Pyran-2-one) Halides
作者:Ian J. Fairlamb、Feng Ju Lu、Jan Peter Schmidt
DOI:10.1055/s-2003-42405
日期:——
The 2-pyrone sub-unit is found in a large number of natural products possessing broad-spectrum biological activity. As such, efficient synthetic methods are required to enable facile access to substituted 2-pyrone derivatives. Important conditions for the Sonogashira alkynylation of 4-bromo-6-methyl-2-pyrone (3a) have been developed, and compared against Negishi’s methodology. The best conditions for Sonogashira alkynylation was found to be the use of Pd/C with added Ph3P as the catalyst, in the presence of catalytic CuI, in a mixture of MeCN and Et3N at reflux. Using Negishi’s standard conditions, terminal alkynylzinc reagents, generated in situ from terminal alkynes with LDA or n-BuLi and subsequent reaction with anhydrous ZnBr2, were reacted with 3a at room temperature using Pd(PPh3)4 as the catalyst in THF.
Halogenated-2-pyrones in Sonogashira cross-coupling: limitations, optimisation and consequences for GC analysis of Pd-mediated reactions
作者:Ian J.S. Fairlamb、Adam F. Lee、Faidjiba E.M. Loe-Mie、Elina H. Niemelä、Ciara T. O'Brien、Adrian C. Whitwood
DOI:10.1016/j.tet.2005.07.102
日期:2005.10
(14) and to a lesser extent (E) and (Z)-ethyl 3-iodo-2-propenonate (16) under similar conditions. A more efficient quenching system (using excess dppe) has been developed to enable accurate determinations in product conversions. Alternatively, solvent and base (Et3N) removal in vacuo, or quench with saturated aqueous ammonium chloride, prevents further turnover in Sonogashira coupling. An ESI-MS study