No abstract

A series of nine TADDOLs ( a,a,a',a'-tetraaryl-1,3-dioxolane-4,5-dimethanols) 1a ± 1i, have been tested as proton sources for the enantioselective protonation of the Li-enolate of 2-methyl-1-tetralone ( 3,4-dihydro-2-methylnaphthalen-1(2H)-one). The enolate was generated directly from the ketone (with LiN(i-Pr) 2 (LDA)/ MeLi) or from the enol acetate (with 2 MeLi) or from the silyl enol ether (with MeLi) in CH 2 Cl 2 or Et 2 O as the solvent (Scheme). The Li-enolate (associated with LiBr/LDA, or LiBr alone) was combined with 1.5 ± 3.0 equiv. of the TADDOL at À 788 by addition of the latter or by inverse addition. 2-Methyl-1-tetralone of (S)-configuration is formed ( 80% yield) with up to 99.5% selectivity if and only if (R,R)-TADDOLs (1d, e, g) with naphthalen-1-yl groups on the diarylmethanol unit are employed (Table). The reactions were carried out on the 0.1-to 1.0-mm scale. The selectivity is subject to non-linear effects (NLE) when an enantiomerically enriched TADDOL 1d is used (Fig. 1). The performance of TADDOLs bearing naphthalen-1-yl groups is discussed in terms of their peculiar structures (Fig. 2).

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