Reduction of 3-Substituted 1-Arylcyclobutanols

Abstract

421In the context of our work on novel model compounds for liquid crystals which contain cyclobutyl groups, [1 -4] we were interested in an effective benzylic alcohol →hydrocar-bon conversion of 1-arylcyclobutanols 1 to give compounds 2. Ideally this should be a one-pot process.Hydrogenolysis as well as elimination/catalytic hydrogenation led to unpleasant product mixtures frequently. Likewise, Olah's method (Pd/cyclohexene/AlCl 3 ) [4] or our own previous procedure (Me 2 NBH 2 /TiCl 4 ) [5] gave unsatisfactory yields oftentimes. When, however, compound 1a was treated with lithium aluminumhydride/aluminum trichloride in tert-butyl methyl ether according to Brewster et al. [6], 2a was obtained in 51% as a 58:42 mixture of trans and cis isomers. Both chemical yield (93%) and stereoselectivity (7:3) where improved when applying a modification of the method of Gribble et al. (NaBH 4 in CF 3 COOH) [7,8].Consequently, this last mentioned procedure was applied to an entire series of 3-substituted 1-arylcyclobutanols 1a -1o. A preponderance of the desired trans isomers (52 -76%) was observed in all cases, and most chemical yields were satisfactory (Table 1) Abstract. A useful and specific method for the the title reaction (1 → 2) involves treatment with NaBH 4 in CF 3 COOH whereas other procedures from the literature yield hard-toseparate mixtures.