Linear Coupling of Three CO Ligands of Chromium Hexacarbonyl Leading to Functionalized Butenolides via Fischer Carbene Complexes

Group 6 Fischer carbene complexes: “chemical multitalents” for multi-component reactions

“…were used, a different pathway takes place affording five-component butenolides 244 in moderate to good yields as a mixture of two isomers (Scheme 42) [73b,75,76]. This MCR involves the participation of two molecules of CO from the coordination sphere of the starting chromium carbene complex, the Scheme 41.…”

New Reactivity Modes of Chromium(0) Fischer Carbene Complexes: Unprecedented Insertion of a Carbene Ligand into an Active B−H Bond

“…Thus, we have reported that the addition of NaBH 4 to alkenylcarbenes 1 is not a simple hydride addition to the M−C bond to yield allyl ethers 2 . The process occurs by the initial 1,2-addition of hydride followed by a 1,3-metal rearrangement, yielding an anionic σ-complex that finally leads to vinyl ethers 3 as the major reaction products. 12a,b A similar mechanism has been proposed to account for the reduction of alkynyl Fischer carbene complexes under the same conditions (Scheme ). Other products derived from the insertion of the carbene ligand into the B−H bond of the reagent were not detected in any case.…”

“…During our ongoing project devoted to study transition-metal-catalyzed carbene transfers from Fischer carbene complexes, we have described the low-temperature cyclopropanation of olefins, a reaction that generally requires harsh reaction conditions to occur. In parallel, our work directed toward an understanding of the factors controlling the addition of nucleophiles to α,β-unsaturated complexes 9 (including the addition of radicals 10 and SET processes 11 ) has resulted in the disclosure of the participation of the metal center in the addition of hydrides to α,β-unsaturated group 6 carbene complexes . Thus, we have reported that the addition of NaBH 4 to alkenylcarbenes 1 is not a simple hydride addition to the M−C bond to yield allyl ethers 2 .…”

One pot synthesis of nitrogen-containing polycyclic δ-lactones by double nucleophilic addition of bis(trimethylsilyl)ketene acetals to pyridinesAll new compounds described in this paper were fully characterized by 200 and 400 MHz 1H NMR, 50 or 100 MHz 13C NMR, mass spectrometry and/or elemental analyses.

“…A further possibility existed for the transformation of the acids 5 into lactones: the oxidative cyclization via the epoxidation of one of the double bonds of the dihydropyridines 5. 4,5 Thus, when the same mixture originating from the monoaddition of the ketene acetals 2a to pyridine was subjected to a mchloroperbenzoic acid oxidation, at room temperature, a new compounds 7a was isolated after silica gel chromatography in 75% yield, as a solid, mp 130° C. Its NMR spectra∑ confirmed the presence of two rotamers, the 13 C NMR spectrum of 7a differing from the spectrum of 6a by the shift of one signal from d 13.6 (C-I) to d 45.6, confirming the formation, upon cyclization, of a secondary alcohol.…”

“…These results and our current interest in the synthesis and uses of dihydropyridines [5][6][7] prompted us to extend a similar methodology for the transformation of pyridines. Three reasons guided this choice: first, the double bonds of pyridine, in contrast to those of the above unsaturated systems, are very readily activated towards nucleophilic additions via pyridinium derivatives, e.g.…”