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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.
Protodemetallation of (Z)-1-aryl-2-germyl-1-stannylethenes using hydrochloric acid in the presence of tetraethylammonium chloride (TEACl) proceeds at 0 • C with retention of configuration to afford trans-1-aryl-2-germylethenes with high yields. In contrast, the reaction using hydroiodic acid in the presence of tetrabutylammonium iodide (TBAI) brings about a novel 1,2-germyl migration accompanying the destannylation to form 1-aryl-1-germylethenes. These 1,2-germyl migration products result with especially high selectivity from adducts bearing a substituent at the ortho-or para-position on the aromatic ring in the adduct. However, the germyl(stannyl)ethenes bearing a substituent at the meta position on the ring produce a regioisomeric mixture of a trans-germylethene and a 1-aryl-1-germylethene.
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