Rhenium- and manganese-catalyzed carbon–carbon bond formation using 1,3-dicarbonyl compounds and alkynes

Abstract

A rhenium complex, [ReBr(CO) 3 (thf)] 2 , catalyzed insertion of terminal alkynes into a C-H bond of active methylene sites of 1,3-dicarbonyl compounds. When a catalytic amount of isocyanide or molecular sieves was added to the reaction mixture, the reaction course changed markedly, and insertion of alkynes into a C-C single bond between αand β-positions of cyclic and acyclic β-keto esters occurred. The formed acyclic δ-keto esters could be converted to 2-pyranones, which were applied to the synthesis of multisubstituted aromatic compounds via the Diels-Alder reaction and successive elimination of carbon dioxide. In the case of the rhenium-catalyzed reactions between terminal alkynes and β-keto esters without substituent at the α-position, tetrasubstituted benzenes were produced regioselectively by two-to-one reaction of the components. The yields of tetrasubstituted benzenes were improved by using a manganese catalyst.Scheme 5 Proposed mechanism for the synthesis of tetrasubstituted benzenes. Scheme 6Proposed mechanism for the synthesis of 2-pyranones.

Organic Reactions Catalyzed by Rhenium Carbonyl Complexes

“…Nakamura and co-workers reported indium-catalyzed addition of active methylene compounds to alkynes . A similar reaction also occurs when the rhenium complex [ReBr(CO) 3 (thf)] 2 is used as the catalyst (eq 15). , This reaction proceeds even with unactivated alkynes, although only terminal alkynes can be used. …”

“…An intramolecular version of this transformation (Conia-ene type reaction) that yields methylenecycloalkanes has also been investigated (eq 16). , Similar reactions are also promoted by gold, nickel/ytterbium, copper/silver, and zinc catalysts. …”

“…In this reaction, two aryl groups of the product orient in the para -position with respect to each other. The manganese complex MnBr(CO) 5 has independently been shown to exhibit higher catalytic activity in this transformation by the same research group , and by Tsuji and Nakamura’s group . To explain the regioselective formation of the tetrasubstituted aromatic compounds, there are two possible reaction pathways (Scheme ).…”

“…They concluded that the reaction proceeds via this route. The second possibility is that the reaction occurs via the formation of a metalacyclopentene intermediate that is produced from a 1,3-dicarbonyl compound and an alkyne (Scheme , path B) …”

Manganese/bipyridine-catalyzed non-directed C(sp3)–H bromination using NBS and TMSN3

“…Manganese is one of the most abundant and nontoxic transition metals found in the earth's crust and its corresponding complexes and salts are useful in synthetic organic reactions [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. Highly reactive and selective bromination reactions have been achieved using a stoichiometric amount of MnO 2 [44] or a catalytic amount of Li 2 MnO 3 [45] under fluorescent light irradiation in the presence of Br 2 (Scheme 1d).…”