M. Novikov, A. Khlebnikov, M. A. Egarmin
Dec 1, 2006
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Influential Citations
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Journal
Russian Journal of Organic Chemistry
Abstract
N-Substituted 9H-fluoren-9-imines react with difluorocarbene to give the corresponding iminium ylides whose further transformations in the absence of active dipolarophiles depend on the substituent at the nitrogen atom and reaction conditions. N-Ethyl-, N-benzyl-, and N-(2-phenylethyl)-9H-fluoren-9-imines are thus converted in low yield into the formal cyclodimerization products and/or 9H-fluorene-9-carboxamides. N-Methyl-substituted fluoreniminium ylide readily adds at the C=N bond of initial N-(9H-fluoren-9-ylidene)-methanamine with formation of spiro-fused imidazolidine derivative; in the presence of fluorenone, acetaldehyde, or benzaldehyde, addition at the C=O group of the dipolarophile occurs to give the corresponding oxazolidine derivatives. The regioselectivity of the cycloaddition of iminium ylides having a fluorene fragment at a double carbon-heteroelement bond can be described by quantum-chemical calculations in terms of the density functional theory (DFT; local hard and soft acids and bases concept): the cycloaddition leads preferentially to the 2,2-difluoro-substituted adduct.