C-Se Bond Formation

Tab. 1. Ipso nucleophilic aromatic substitution of arenetricarbonylchromium complexes C-O, C-S and C-Se bond formation.

The structures of organic selenium compounds are closely related to those of the homologous sulfur compounds. However, in sharp contrast to organosulfur compounds, most of the organoselenium derivatives contain the divalent, dicoordinate selenium atom. Tetravalent, tricoordinate selenium compounds such as selenoxides, selenonium salts and seleninic acids are much less common. Only a few hcxavalent selenium compounds such as selenonic acids and selenones are known. Thus, asymmetric C —Se bond formation is limited to creation of a carbon — selenenyl bond. 

The BiBrs-Sm binary reagent promotes reductive C-S and C-Se bond formation between benzyl and allyl bromides and diorganyl disulfides and diselenides in aqueous media, affording the corresponding sulfides and selenides, respectively (Scheme 14.105) [217, 218]. Intramolecular reductive C-S bond formation by use of a BiCl3-M (M = Sn, Zn) redox system is used in the synthesis of 3-hydroxyceph-ems and 2-exo-methylenepenams (Scheme 14.106) [219]. Alkyl and arylsulfonyl chlorides couple with allylic halides in the presence of Bi to afford the corresponding allylic sulfones [220]. 

The various selenenylation reagents shown in Part B of Scheme 5.1 are characterized by an areneselenenyl group substituted by a leaving group. Some of the fundamental mechanistic aspects of selenenylation were established by smdies of the reaction of E-and Z-l-phenylpropene with areneselenenyl chlorides. The reaction is accelerated by an ERG in the arylselenenides. These data were interpreted in terms of a concerted addition with ionization of the Se-Cl bond leads C—Se bond formation. This accounts for the favorable effect of ERG substituents. Bridged seleniranium ions are considered to be intermediates. 

Little C—Se bond formation by palladium catalysis has been reported, although these reactions should be feasible considering the ability of palladium complexes to catalyze C—S, C—P, and C—As bond formation. However, nickel complexes have been used for carbon-selenium bond formation. In 1985, Cristau and co-workers used bis(bipyridyl)nickel(ll) bromide to form aryl selenides from aryl halides and sodium benzeneselenoate. ... 

Route 1 involves an initial migratory arylzincation pathtvay that is followed by a copper-mediated reaction with elemental sulfur, with accompanying C-S cyclization to afford a substituted benzothiophene in a one-pot reaction. Alternatively, in route 2, the zinc intermediate is first trapped by iodine, and subsequent copper-catalyst allows C-S/C-Se bond formation followed by cyclization in the presence of elemental sulfur or selenium to afford the corresponding benzochalcogenophene. A modular two-step synthesis of dithieno[3,2-l) 2, 3 -d]thiophene derivatives by C-S cross-coupling and oxidative dehydro C-H coupHng was also described in the year 2014 (14OL4086). 

A final set of studies by Canty focused on C-Se bond formation from the mixed... 

Beletskaya IP, Anailkov VP. Unusual influence of the structure of transition metal complexes on catal3ftic C—S and C—Se bond formation under homogeneous and hetereogeneous conditions. Eur. J. Org. Chem. 2007 3471-3444. 

Beletskaya IP, Ananikov VP (2007) Unusual influence of the structures of transition metal complexes on catalytic C-S and C-Se bond formation under homogenous and heterogeneous conditions. Eur J Org Chem 3431-3444... 

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