Rhodium‐Catalyzed Asymmetric Allylation of Malononitriles as Masked Acyl Cyanide with Allenes: Efficient Access to β,γ‐Unsaturated Carbonyls

Abstract

A rhodium-catalyzed regio- and enantioselective intermolecular allylation of malononitriles as masked acyl cyanides (MAC) with terminal and symmetrical internal allenes is reported. A Rh /Josiphos catalytic system combined with subsequent oxidative degradation of the primary adducts enables a straightforward access to α-branched, β,γ-unsaturated carbonyl compounds. The present protocol exhibits perfect atom economy in the allylation step and is characterized by a great functional group compatibility. Furthermore, the use of α-substituted malononitriles allowed for the construction of all-carbon quaternary centers.

Metal-Catalyzed Intermolecular Hydrofunctionalization of Allenes: Easy Access to Allylic Structures via the Selective Formation of C–N, C–C, and C–O Bonds

“…In the same year, the group of Breit employed malonitrile as dicarbonyl compounds and performed allylation with a rhodium/Josiphos-type ligand catalyst with excellent enantioselectivity (Scheme 67). 156 The reaction scope was quite large and tolerated many functionalities on the starting 1,3disubstituted allenes. Furthermore, authors performed oxidative cleavage of the synthesized substituted malonitriles to obtain β,γ-unsaturated methyl esters.…”

Promoting Thermodynamically Unfavorable [3,3] Rearrangements by Chemoselective Reduction

“…The original Cope rearrangement − substrates, 3,3-dicyano-1,5-dienes 1 , are attractive building blocks for chemical synthesis. They are prepared from ketones/aldehydes, malononitrile, and an allylic electrophile by Knoevenagel condensation then deconjugative alkylation, − and are thermally reacted to form γ-allylalkylidenemalononitriles 2 at temperatures ranging from room-temperature to 150 °C. − ,,,− Furthermore, Cope products can be converted into diverse scaffolds in rapid fashion; e.g., densely functionalized cycloheptenes ,,− and linear carboxylate derivatives. − …”

“…By malononitrile allylation and ring-closing metathesis (RCM), 5–7 (hydroazulenes) and 6–7 scaffolds of 3 can be accessed (Scheme A) . Monoalkylmalononitriles can also be converted readily to esters by oxidative esterification. − For example, the reduced Cope product H 2 -2b was converted to the exomethylenecyclopentane-ester building block 4a when magnesium monoperoxyphthalate (MMPP) was utilized as an oxidant in methanol . Such scaffolds may find value in hydrindane synthesis (e.g., 5 ) by a Prins-like cyclization (Scheme B). , A few other exomethylenecycloalkane-ester building blocks 4b–4d were prepared by oxidative decyanation in modest to excellent yields.…”

Rhodium-Catalyzed Enantioselective Cyclization of 3-Allenyl-indoles: Access to Functionalized Tetrahydrocarbazoles

“…Despite their respective synthetic utility and their excellent stereoelectivities, these methods represent allylic substitution reactions and thus violate the principle of atom economy by releasing stoichiometric amounts of a side product in the course of the reaction. Throughout the last years, we reported on a series of intermolecular rhodium-catalyzed chemo-, regio-, and enantioselective coupling reactions involving allenes , and alkynes , as allylic electrophile precursors with various pronucleophiles, thus establishing a more atom-economic alternative to the classic allylic alkylation. Meanwhile, we were also able to expand this methodology toward asymmetric intra molecular transformations …”