Le rearrangement de claisen en series siliciee et germaniee: silaethylene et germaethylene

Palladium-Catalyzed Intramolecular Hydrosilylation of Alkenylsilanes: Selective Formation of Six-Membered Silicon Heterocycles

“…Evaporation of solvent and flash chromatography of the residue gave 1-methyl-1phenylsilacyclohexane (4) in 87% yield (Scheme 2). Significantly, GC, 1 H NMR, and 13 C NMR analysis of the crude reaction mixture revealed no detectable concentration of 1,2-dimethyl-1-phenylsilacyclopentane (5). The 1,1′-bipyridyl complex (bipy)PdMe(OEt 2 ) + B-Ar 4also catalyzed the cyclization of 3 to form a 16:1 ratio of 4:5 in 83% yield (Scheme 2).…”

“…All reactions were performed under an atmosphere of nitrogen employing standard Schlenk techniques. NMR spectra were obtained on a General Electric QE 300 spectrometer operating at 300 MHz for 1 H and 75 MHz for 13 C in CDCl3 unless otherwise noted. Gas chromatography was performed on a Hewlett-Packard 5890 gas chromatograph equipped with a 25 m poly(dimethylsiloxane) capillary column.…”

“…In contrast, 4-pentenylsilanes or 3-butenylsilyl ethers are converted selectively to six-membered silicon heterocycles only when the internal olefinic carbon atom bears substitution . Furthermore, selective conversion of 5-hexenylsilanes or 4-pentenylsilyl ethers to six-membered silacycles has not been demonstrated . For example, reaction of dimethyl-5-hexenylsilane with chloroplatinic acid forms a ∼1:1 mixture of six- and seven-membered silacycles in 70% yield (eq 2) …”

“…12 Furthermore, selective conversion of 5-hexenylsilanes or 4-pentenylsilyl ethers to six-membered silacycles has not been demonstrated. 13 For example, reaction of dimethyl-5-hexenylsilane with chloroplatinic acid forms a ∼1:1 mixture of six-and seven-membered silacycles in 70% yield (eq 2). 1 Cationic Pd(II) complexes employed in conjunction with weakly coordinating counterions possess high activity with respect to olefin β-migratory insertion 14 and have been employed as catalysts for the polymerization of R-olefins 15 and for the copolymerization of ethylene and CO. 16 These complexes also cleave Si-H bonds via low-energy σ-bond metathesis pathways and have been employed as olefin hydrosilylation catalysts.…”

Highly selective metal mediated ortho-alkylation of phenol. First platinum containing organometallic chromane analogues

“…This excludes a priori a possible mechanism involving an intramolecular Claisen-type rearrangement, previously reported for the formation of Si and Ge chromane derivatives. 19 Noteworthy the present highly selective metal mediated orthoalkylation of the phenol also represents a new synthetic application of olefin containing cationic species, 22 [PtCl(g 2 -olefin)(N-N)] + , since in their derivatives [Pt(g 1 -CR 1 R 2 -CR 3 R 4 -Nu)Cl(N-N)], R 1-4 = H or alkyl, one end of the former olefin proved to be characterized (at least in the cases of [Pt(g 1 -C 2 H 4 OR)Cl(phen)], R = Me or Ph) by an incipient carbo-cationic character.…”