Divergence of Carbonyl Ylide Reactions as a Function of Diazocarbonyl Compound and Aldehyde Substituent:  Dioxolanes, Dioxolenes, and Epoxides

Abstract

The products from dirhodium(II) acetate-catalyzed reactions between diazocarbonyl compounds and a series of benzaldehydes demonstrate the extent of competition between intramolecular and intermolecular trapping of carbonyl ylide intermediates and the electronic effects that govern these transformations. With dimethyl diazomalonate, competition exists between dioxolane and epoxide formation so that with p-anisaldehyde only epoxide formation is observed and with p-nitrobenzaldehyde only 1,3-dioxolane products are formed. With methyl diazoacetoacetate, intramolecular trapping of the intermediate carbonyl ylide results in the sole production of dioxolenes. However, the vinyldiazoacetate analogue of methyl diazoacetoacetate, as its tert-butyldimethlsilyloxy derivative, only produces epoxides in its reactions with substituted benzaldehydes.

[2 + 1] Cycloaddition of Catalytic Ruthenium Vinyl Carbenes: A Stereoselective Controlled Access to (Z)- and (E)-Vinyl Epoxypyrrolidines

“…Based on our previous results and labeling experiments, we propose the following mechanism for the Ru-catalyzed epoxy-annulation (Scheme ). The starting complex, [Cp*RuCl­(cod)], easily loses its cod ligand in the presence of TMSCHN 2 , with the concomitant release of N 2 , and binds to the alkynal to give the ruthenium carbene species I , which would directly evolve to the coordinatively saturated ruthenium vinyl carbene species II . , This electrophilic species could induce a nucleophilic attack by the carbonyl group to afford the zwitterionic intermediate III , which finally collapses to the observed epoxypyrrolidine . In this case, intermediate III cannot evolve by deprotonation/protonation steps, because of a lack of hydrogens (or sterically encumbered) at the α-position, which blocks the formation of the dihydrooxazine .…”

Cp*RuCl‐Vinyl Carbenes: Two Faces and the Bifunctional Role in Catalytic Processes

“…The two possible pathways arising from the nucleophilic addition of the carbonyl group to both sterically differentiated faces of the initially formed [Cp*RuCl] h 3 -vinylcarbene A were computed ( Figure 5). [30] Interestingly, the nucleophilic addition of the carbonyl to the ruthenium carbene throught he Re face is significantly more favorable than the addition through the Si face ( Re TS A_B vs. Si TS A_B ). Moreover,y lide intermediate Re B is 14.1 kcal mol À1 more stable than ylide Si B.S uch remarkable difference in energy cannotb e only attributedt oa ni ncreased steric hindrance through the Si face of the carbene;t hus, ac loser examination of the structures of both transition states and intermediates revealed an unexpected contribution of the Cl ligand ( Figure 6): i) in the A!…”

The interaction of rhodium carbenoids with carbonyl compounds as a method for the synthesis of tetrahydrofurans

“…The early investigations by Huisgen and de March [19] with dimethyl diazomalonate (1) revealed that in reactions with benzaldehyde, a mixture of isomeric 1,3-dioxolanes (2) was formed (Scheme 1) when Rh 2 (OAc) 4 , Cu(acac) 2 or CuOTf was used as the catalyst. Since the initial Huisgen report, the catalytic generation of carbonyl ylides from diazo compounds has developed into a powerful reaction for organic synthesis [20][21][22].…”