Synthesis and characterization of (-)-1-menthyl-4,7-dimethylindene and itsmain group metal compounds with lithium, sodium, potassium, and tin

(-)-3-Menthyl-4,7-dimethylindene and (-)-4,7-diisopropyl-3-menthylindene we re prepared in 63 and 48% yield, respectively, through a 1,1'-bis(diphenylp hosphino)ferrocene-pall catalyzed cross-coupling reaction of menthylzinc wi th 3-(4,7-dimethylindenyl) trifluoromethanesulfonate or 3-(4,7-diisopropyli ndenyl) trifluoromethanesulfonate. Several other methods including addition of menthyl Grignard to 1-indanone, addition of (indenyl)lithium to menthon e, or coupling of 3-bromoindene with menthyl Grignard for preparing 1-(or 3 -)-menthylindene were inferior to direct substitution of menthyl-sulfonate esters by (indenyl)lithium. (-)-3-Menthyl-4,7-dimethylindene could be depro tonated to form a single diastereomeric lithium salt that was characterized by X-ray crystallography. (-)-4,7-Diisopropyl-3-menthylindene was deproton ated to form a lithium salt. Formation of the sodium and potassium salts of (-)-3-menthyl-4,7-dimethylindene was possible, but the products were not s tereochemically characterized. 1-Trialkyltin compounds with (-)-3-menthyl-4 ,7-dimethylindene were prepared as nearly 1:1 diastereomeric mixtures from the lithium salt.