SAMARIUM(II) TRIFLATE AS A NEW REAGENT FOR THE GRIGNARD-TYPE CARBONYLADDITION-REACTION

On treatment of a THF solution of Sm(OTf)(3) with 1 equiv of an organo lithium or organomagnesium reagent-at ambient temperature, the purple or deep green solution of the divalent samarium triflate [Sm(OTf)(2)] was readily obtained. For this preparation, s-BuLi was the most effect ive as was evidenced by the reduction of a-phenylethyl iodide in the p resence of HMPA. The Sm(OTf)(2) reagent mediated the Grignard-type rea ction effectively in THF/HMPA; alkylation and allylation of ketones or aldehydes with alkyl, allyl, or benzyl halides proceeded via organosa marium intermediates. Diastereoselectivity of the samarium-Grignard re action was examined using 2-methylcyclohexanone, 4-tert-butylcyclohexa none, and 2-phenylpropanal and was found to be higher in each case tha n that with SmI2. With 2-methylcyclohexanone, for example, Sm(OTf)(2) gave the greatest ratio of axial alcohol:equatorial alcohol = 99:1, an d SmI2 gave a ratio of 91:9. Halides containing an ester or a silyl gr oup were reactive in the Reformatsky- or Peterson-type reaction, respe ctively, using the Sm(OTf)(2) reagent.