Allenes reactions with Fischer carbene complexes

Dienes. The reaction of Fischer carbene complexes with allenes gives 1,3-dienes into which the nonmetal moiety is incorporated. The transformation is a formal ene-type process. 1-Alkoxy-1,3-dienes arise when the carbene complexes and propargylsilanes are heated together. A 1,2-silicon shift accompanies the carbene insertion into the C-H bond. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

The corresponding [3 + 2 + 2]- and [2 + 2 + 2 + l]-cyclization reactions between these complexes and alkynes are very efficient in the presence of Ni(0). Transmetallation reactions between chromium Fischer carbene complexes and Ni(cod)2 with formation of nickel carbene intermediates is presumed to be responsible for this transformation. The metal-free cycloadducts are easily obtained by ligand exchange reactions at low GO pressures. A [3-h2]-cyclization reaction of a chromium Fischer carbene complex and allene building blocks was accomplished, using... 

Chromium alkenyl Fischer carbenes have been shown to undergo a 3 + 2-cyclization with allenes under Rh(I) catalysis and a CO atmosphere, yielding 2-alkylidenecyclo-pentanone (54) after acidic hydrolysis.46 Reactions with electron-rich allenes are carried out with a neutral rhodium complex whereas electron-poor allenes require a... 

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