Stereoselective synthesis of unsymmetrical conjugated dienes and trienes utilizing silacyclobutenes

Efficient One‐Pot Synthesis of N‐Containing Heterocycles by Multicomponent Coupling of Silicon‐Tethered Diynes, Nitriles, and Isocyanides through Intramolecular Cyclization of IminoacylZr Intermediates

“…Isolation and structural characterization of iminoacylÀZr and bis(iminoacyl) À Zr intermediates through mono-and double-insertion of isocyanides into azazirconacycles: Green solids 2 that have a reactive Zr À CA C H T U N G T R E N N U N G (sp 3 ) s bond could be isolated in high yields from the zirconocene-mediated coupling of the silicon-tethered diyne and iPrCN (Scheme 2). [15,17] Treatment of 2 a with 1.2 equivalents of aliphatic isocyanide tBuNC at room temperature for 1 h cleanly led to the mono-insertion of tBuNC into the ZrÀCA C H T U N G T R E N N U N G (sp 3 ) s bond to give 3 a in 91 % isolated yield (Scheme 2 a). Even in the presence of 2.4 equivalents of tBuNC, only 3 a was obtained and the double-insertion product was not observed, probably owing to the steric hindrance of tBu group.…”

Formation of α‐Lithio Siloles from Silylated 1,4‐Dilithio‐1,3‐Butadienes: Mechanism and Applications

“…1,4-Dihalo-1,3-butadiene compounds are prepared, unless otherwise mentioned, by the reported methods. [14e, 15] 1 H and 13 C NMR spectra were recorded at 300 and 75.4 MHz, respectively, in CDCl 3 unless stated otherwise.…”

“…Di-iodides 4 d-e can be easily obtained from diynes 8 a-b by the known method as illustrated in Scheme 4. [13][14][15] Lithiation of these di-iodides could give the corresponding dilithio reagents 1 d-e, which would undergo similar transformation to give silole derivatives as the only products (Scheme 5). For example, dilithio reagent 1 d would convert into a-silylated silole 3 d in excellent yield at room temperature after quenching with water.…”

“…The solvent was evaporated in vacuum, and the residue thereafter was purified by column chromatography using silica gel to afford the tetra-iodide products 4 g-i. 13 To a solution of 2-iodothiophene (2 mL, 105 mg, 0.5 mmol) in THF, was added tBuLi (0.63 mL, 1 mmol, 1.6 m in pentane) at À78 8C. After stirring for 0.5 h, a solution of ZnCl 2 (82 mg, 0.6 mmol) in THF (2 mL) was added.…”

“…After the removal of n-hexane, the final product 2 a was obtained by recrystallization from hexane as colorless crystals, 2 a (190 mg, 92 %). 1 H NMR (300 MHz, C 6 D 6 , 258C): d = 0.42 (s, 9 H; CH 3 ), 0.73 (s, 6 H; CH 3 ), 1.14 (t, J = 6.9 Hz, 6 H; CH 3 ), 3.37 (q, J = 6.9 Hz, 4 H; CH 3 ), 7.18-7.47 ppm (m, 10 H; CH); 13 X-ray Crystallographic Studies of 2 a…”