2-furyl-carbene complexes

Three-memberedRings. [2 + 1] processes Several examples of PdCl2-catalyzed cascade cyclopropanation processes have been reported in the literature. Thus, enyne ketone reacted with styrene in the presence of PdCl2 to afford the cyclopropanated product in excellent yield and in high diastereoselectivity (eq 71) via a palladium 2-furyl carbene complex. 

Vinyl-substituted benzo[c]furans can be prepared by reaction of n-alkynylbenzaldehydes with chromium Fischer carbene complexes. Initially a benzo[c]furan chromiumtricarbonyl complex is believed to be formed which is converted into an alkylidenephthalan derivative or can be trapped with electron-deficient dienophiles with excellent ( 3 ti-selectivity (Equation 128) <20000L1267>. More elaborate vinylidene Fischer carbene complexes yield dienyl benzo[c]furans that undergo [8-1-2] cycloaddition with DMAD to furnish furanophane derivatives <2003JA12720>. An equilibrium between 7] -(o-ethynylbenzoyl)rhenium complexes and rhenium benzo[f]furyl carbene complexes has been observed. These species behave like other benzo[< ]furans in the reaction with DMAD <20040M4121>. 

Chiral Fischer-type (menthyloxy)(3-furyl)carbene complexes underwent nucleophilic 1,4-addition with lithium reagents in a regioselective and diastereoselective manner. In particular, a reaction with (Z)-2-phenylethenyllithium provided the (Z)-alkene product shown below in excellent %ee <03CEJ5725>. 

The following is a complete list of citations describing the benzannulations of furyl carbene complexes refs. 82,99,107,118,119,121,130, 132 and 133. 

Two research groups independently extended the electrocyclization system into the stoichiometric formation of pyranylidene complexes (25 and 27), which also proceeds via vinylidene complexes as key intermediates (Scheme 21.10) [16,17], Further reactions of the pyranylidene complexes 25 with a variety of alkenes gave the corresponding naphthalenes 28 in good to high yields. In addition, Miki and others found the catalytic formation of cyclopropanes bearing a furan ring 30 from reactions of ene-yne ketones 29 with a variety of alkenes, where furyl carbene complexes 31 were proposed as key intermediates (Scheme 21.11) [18],... 

Experimental Procedure 2.2.9. [4 + 3] Cycloaddition of a Chromium Carbene Complex to a 2-Aminodiene 6-(2-Furyl)bicyclo[5.4.0]undecan-2,4-dione [264]... 

The new class of carbene complexes, acyloxy-carbenes [(CO)sCrC(X)OAc] (X = 2-furyl or CH2SiMe3) have been isolated. These compounds extend the synthetic range of these carbene systems and afford the nitrile [(CO)5CrNCC4-H3O] and isonitrile [(COijCrCNMe], respectively, with HN3. ... 

Surprisingly, the reactipn of (C0)5Cr[C(0)furyl] "Li with (Me3Si)3SiBr in ether to give (CO)5Cr C[OSi(SiMe3)3]furyl is reversible and results in an equilibrium. However, using the tetramethylammonium instead of the lithium salt the conversion of the acylate complex to the carbene complex is quantitative. ... 

The common alkyne trapping reagent 1,3-diphenylisobenzofuran was used as a precursor towards the synthesis of new analogs of famesyltransferase inhibitor RPR 130401 <04JOC7220>. A rhenium isobenzofuryl carbene complex was also synthesized recently <04OM4121>. As depicted below, thermal rearrangement of the ri -(o-ethynylbenzoyl)-rhenium complex produced the benzo[c]furyl rhenium carbene complex, presumably via a nucleophilic attack of the carbonyl oxygen on the rhenium-bound alkyne. The alkyne rhenium complex and the rhenium carbene complex were both observed at equilibrium. Like all other benzo[c]furans, the rhenium isobenzofuryl carbene species reacted smoothly with... 

Cyclopropanation proceeds through the formation of an electrophilic (2-furyl)carbene-chromium complex which in turn forms through 5-exo dig cyclization. As shown in Scheme 10.13, cyclization of ene-yne-ketone 15 begins with the nucleophilic attack of carbonyl oxygen to an internal carbon of an alkyne in q -alkyne complex A. A might be the most plausible pathway for generation of (2-furyl)carbene-chromium complex 18. A slipped, polarized q -complex B would be an alternatively possible intermediate. It is known that A is prone to isomerize to B, which has been... 

Here HY is a proton donor and Z is a proton acceptor— in most cases these roles are performed by the amine and/or the solvent. All these reactions have a negative activation energy, and all the experimental observations can be accommodated by the mechanism shown in the Scheme. The same carbene complex, Cr(CO)s C(OMe)Ph, reacts with aminoethanol in two ways, to produce (14) and (15). Both are formed by attack at the carbene-C (14) arises from attack by HN=CHMe (aminoethanol minus the elements of water), and (15) from attack by NHg (aminoethanol minus the elements of acetaldehyde). The compound Cr(CO)6 acetoxy-(2-furyl)carbene reacts with hydrazoic acid to give Cr(CO)5(2-furonitrile). 

Optically active furyl cyclopropane 402 was prepared from acetylene dicarboxylate and alkenes (Scheme 1.187) [261]. The acetylene dicarboxylate underwent dimerization to form metallocyclopentadiene 403, which decomposes to give cyclopropanes containing rhodium carbene complex 404. A good level of chiral induction was achieved using Segphos ligand with Rh(cod)2Bp4. 

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