中文名称 | 英文名称 | CAS号 | 化学式 | 分子量 |
---|---|---|---|---|
—— | 2-(Bromomethyl)-1-{2-[2-(bromomethyl)phenyl]ethyn-1-yl}naphthalene | 223596-86-9 | C20H14Br2 | 414.139 |
The enantioselective [2+2+2] cycloisomerisation of the aromatic triynes under nickel(0) catalysis to afford nonracemic [6]- and [7]helicene derivatives has been systematically studied. A collection of mono- and bidentate phosphines, phosphites, phosphinites and phosphinous amides possessing stereogenic units such as chiral centre, axis or plane (or their combinations) has been tested and axially chiral binaphthyl-derived monodentate MOP-type phosphine ligands were the optimal class of ligands. Nickel complexes of these ligands afforded nonracemic tetrahydro[6]helicene in up to 64% ee in a model reaction.
A general and versatile synthetic approach to a broad series of aromatic triynes as precursors to helicene derivatives has been developed. Employing a set of simple tools, triynes comprising the (phenylethynyl)benzene, 1-(phenylethynyl)naphthalene, and 1-(1-naphthylethynyl)- naphthalene moiety have been prepared in good to excellent yields throughout the whole reaction sequence. The methodology allows constructing various types of a junction between the central diarylacetylene moiety and the attached acetylene units to get the target triynes of general formula R-C≡C-CH2-X-CH2-Ar-C≡C-Ar'-CH2-X-CH2-C≡C-R or R-C≡C-CH2CH2-Ar-C≡C-Ar'-CH2CH2-C≡C-R (R = H, CH3, TMS, or TIPS; X = O, NTs, or C(CO2CH3)2; Ar/Ar' = 2-phenylene or 2-naphthylene).
Triynes R-C≡C-CH2CH2-Ar-C≡C-Ar'-CH2CH2-C≡C-R were subjected to Co(I)- or Ni(0)-mediated intramolecular [2+2+2] cycloisomerization to provide corresponding tetrahydropentahelicene, tetrahydrohexahelicene, and tetrahydroheptahelicene in good to moderate yields. The reaction tolerates various substituents at pendant acetylene moieties (R = H, CH3, trimethylsilyl, not triisopropylsilyl) and fluorine in an aromatic part. By contrast, under Rh(I) or Pd(0) catalysis, triyne with the CH2OCH2 tether lost pendant propargyl moieties and an aromatic spiroketal was formed preferentially.