ALPHA-OXYGEN-SUBSTITUTED ORGANOLITHIUM COMPOUNDS AND THEIR CARBENOID NATURE - REACTIONS WITH RLI AND OTHER NUCLEOPHILES, EXPERIMENTAL AND IGLO-CALCULATED C-13-NMR SHIFTS OF THE CARBENOID-C ATOM

In addition to the earlier[1] demonstrated C-O bond elongation between the anionic carbon atom and oxygen in alpha-lithiated ethers which indicates a carbenoid character of these compounds we provide further evidence for this property in this publication. Thus, alpha-lithiated ethers RCH(Li)-OR' react as electrophiles with nucleophiles R''Li to give RCH(Li)-R'' + LiOR', and the C-13-NMR signal of the carbenoid C atom is shifted downfield (compared to the C-13 signal of the corresponding non-lithiated compound). Since the latter two observations are also made in the Li/Hal carbenoid series, alpha-lithiated ethers indeed are Li/oxygen carbenoids. Furthermore, for the first time we have calculated the C-13 shifts of carbenoid C atoms in the Li/oxygen carbenoid series by means of the IGLO method: the calculated data agree nicely with the experimental ones. They even allow the preferred bridged structure in solution to be determined.