Stereodefined synthesis of an unprecedented family of vinylgermanes bearing an allyl group, (E)-2-aryl-1-germylalka-1,4-dienes, or an allenyl group, (E)-4-aryl-5-germylpenta-1,2,4-trienes, via a cross-coupling reaction of (Z)-germyl(stannyl)ethenes with the respective allyl halide (Br, Cl) and propargyl bromide is described. In the reaction with allyl halides, either a Pd(dba) 2 -CuI combination (dba: dibenzylideneacetone) or CuI alone readily catalyzes or mediates the coupling reaction of (Z)-germyl(stannyl)ethenes, producing the novel vinylgermanes bearing an allyl group. The thienyl group or hydroxy group of the (Z)-germyl(stannyl)ethene survives the reaction. Copper(I) iodide alone readily mediates the reaction with allyl chloride or methallyl chloride upon addition of sodium bromide to produce the respective cross-coupled product in good yield. In contrast, crotyl halides (Br, Cl) or prenyl chloride couple with/without allylic transposition in the bromide or the chloride. In the reaction with propargyl bromide, a Pd(dba) 2 and CuI combination efficiently drives the coupling reaction of (Z)-germyl(stannyl)ethenes in NMP (N-methylpyrrolidone), providing the stereochemically defined allenyl vinylgermanes, (E)-4-aryl-5-germylpenta-1,2,4-trienes, in good yields.
A combination catalyst of Pd(dba) 2 -PPh 3 -CuI-LiCl or Pd(dba) 2 -P(2-furyl) 3 -CuI-LiCl effectively catalyzed the cross-coupling of (Z)-germyl(stannyl)ethenes with aryl halides, providing novel triethyl(2,2-diarylethenyl)germanes in good to high yields. The reaction proceeds with retention of configuration. Cross-coupling results in the formation of phenylene or phenyleneethynylene derivatives with terminal stereochemically defined vinylgermane unit(s).
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