Preparation of seven-membered rings by the reaction of cyclopropylcarbene-tungsten and molybdenum complexes with alkynes

Fischer Carbene Complexes in Heterocyclic Synthesis. Selective Cycloaddition Reactions to 2-Aza-1,3-butadienes

“…Since their discovery in 1966 by Fischer, stabilized Fischer carbene complexes of group 6 have been recognized to play an important role in the construction of a variety of 3- to 7-membered carbocyclic rings and acyclic compounds as well . For instance, reactions involving the carbene ligand of α,β-unsaturated complexes, as the activated two-electron system, have permitted a number of [2+2] 2d,3 and [4 + 2] 4 cycloadditions as well as 1,3-dipolar cycloadditions to be achieved 5 On the other hand, the reactions occurring at the metal center are doubtless more characteristic for these systems, and important carbocyclizations of the type [2 + 1], [2 + 1 + 1], [4 + 1], [3 + 2], , [3 + 2 + 1], [4 + 2 + 1 − 2], [4 + 2 + 1], and [4 + 3] have been reported quite frequently in the last years. The flexibility of these organometallic reagents toward organic substrates has also made them useful tools in natural products synthesis …”

High-Diastereoselective and Enantioselective Cyclopropanation of α,β-Unsaturated Fischer Carbene Complexes: Synthesis of Chiral 1,2-Disubstituted and 1,2,3-Trisubstituted Cyclopropanes

“…Among other interesting properties, the synthetic usefulness of these complexes is due to their rich reactivity, showing their own unique types of reactivity. Specifically, cyclopropylcarbene complexes can be transformed into cyclopentenones, cyclopentadienones, cyclopentane-fused oxygen heterocycles, cycloheptadienones, alkenyl halides, and donor−acceptor-substituted cyclopropanes or photochemical conditions .…”

Reactivity of the Inversely Polarized Phosphaalkene HPC(NMe2)2Toward Carbene Tungsten Complexes [(CO)5WC(R1)OR2] (R1=c-C3H5,c-C5H9; R2= Me, Et, Me3Si): A Novel Access to η1-Phosphaalkene Complexes [(CO)5W−P(R2)C(H)NMe2]

“…Our investigations were extended to cyclopropyl(methoxy)- and cyclopropyl(ethoxy)carbene complexes 11b and 11c . Reaction with equimolar amounts of HPC(NMe 2 ) 2 in n -pentane at −50 °C to room temperature led to the formation of the bis(pentacarbonyl)-1,3-diphosphetane complexes 13b and 13c , which were obtained from pentane solutions at −16 °C as yellow to orange crystals in 60% and 72% yield, respectively.…”

“…Elemental analyses were performed at the microanalytical laboratory of the University of Bielefeld and at Mikroanalytisches Laboratorium H. Kolbe, Mülheim, Ruhr, Germany. Compounds t BuPC(NMe 2 ) 2 ( 6a ), Me 3 SiPC(NMe 2 ) 2 ( 6b ), HPC(NMe 2 ) 2 ( 6c ), [(CO) 5 WC(OMe)( c -C 3 H 5 )] ( 11b ), and [(CO) 5 W(OEt)( c -C 3 H 5 )] 10 ( 11c ) were synthesized according to literature procedures.…”