20.2A Crossed claisen condensations(交叉克菜森缩合) Crossed Claisen condensations are possible when one ester component has no a ydrogens and is, therefore unable to undergo self-condensation ), CH3 OCH, CH,+ CH3 COoCH Ethyl benzoate no a -hydrogen OCH2 CH3 Ethyl benzoylacetate (60%)20.2A Crossed Claisen condensations (交叉克莱森缩合） Crossed Claisen condensations are possible when one ester component has no α- hydrogens and is, therefore, unable to undergo self-condensation. O OCH2CH3 + CH3COOC2H5 1) NaOCH2CH3 2) H + O H2 C O OCH2CH3 Ethyl benzoate Ethyl benzoylacetate (60%)   no  -hydrogen