Catalytic 1,4‐Rhodium(III) Migration Enables 1,3‐Enynes to Function as One‐Carbon Oxidative Annulation Partners in CH Functionalizations

Abstract

1,3-Enynes containing allylic hydrogens cis to the alkyne are shown to act as one-carbon partners, rather than two-carbon partners, in various rhodium-catalyzed oxidative annulations. The mechanism of these unexpected transformations is proposed to occur through double C–H activation, involving a hitherto rare example of the 1,4-migration of a RhIII species. This phenomenon is general across a variety of substrates, and provides a diverse range of heterocyclic products.

Rhodium-Catalyzed Oxidative C–H Allylation of Benzamides with 1,3-Dienes by Allyl-to-Allyl 1,4-Rh(III) Migration

“…Coordination and migratory insertion of 1,3-diene 2d at the less-substituted alkene gives rhodacycle 8, in which there is also an allylrhodium(III) moiety. Acetolysis of 8 gives allylrhodium(III) species 9, which can undergo 1,4-Rh(III) migration 10,11,12 to the cis-allylic carbon to give a into σ-allylrhodium species 12, which undergoes β-hydride elimination to give 3ad (Scheme 4). If this mechanism was operative, it would be expected that dienes 2e and 2h, which differ only in the geometry of the trisubstituted alkene, would react to provide similar outcomes.…”

“…In this reaction, 1,3-enyne 19 functions as a one-carbon annulation partner as a result of an alkenyl-to-allyl 1,4-Rh(III) migration. 10 …”

Arylative Intramolecular Allylation of Ketones with 1,3‐Enynes Enabled by Catalytic Alkenyl‐to‐Allyl 1,4‐Rhodium(I) Migration

“…This new mode of reactivity was employed in the diastereoselective reaction of arylboron reagents with substrates containing a1 ,3-enyne tethered to ak etone,t og ive products containing three contiguous stereocenters.T he products can be obtained in high enantioselectivities using ac hiral sulfur-alkene ligand.CatalyticCÀHfunctionalizationshave revolutionized chemical synthesis by providing powerful new tools for bond construction.[1] However,acritical objective for the advancement of this field is its application to amore diverse range of transformations.N ucleophilic allylations [2] are important reactions that could benefit from C À Hf unctionalization principles.M ost typically,t hese processes have employed allylmetal(loid) reagents such as allyltin, allylboron, or allylsilicon compounds.[2] Theg eneration of nucleophilic allylmetal species by the activation of allylic C À Hb onds would bypass the need to prepare such reagents and potentially increase efficiencyb ys treamlining synthetic sequences.This strategy would also be avaluable complement to nucleophilic allylations involving migratory insertions of allenes, [3,4] theu se of simple p-unsaturated compounds in hydrogenative or redox-triggered additions, [5,6] hetero-ene reactions, [7] and Prins reactions.[8]Although generating electrophilic allylmetal species by allylic CÀHa ctivation is well-known, [9,10] there is,t oo ur knowledge,l imited precedent for corresponding processes that provide nucleophilic allylmetals.[11] Very recently,t he groups of Schneider, [11a] Kanai, [11b] and Mita and Sato [11c] described the formation and trapping of nucleophilic allylmetal species from simple hydrocarbons.I nv iew of the nucleophilic character of allylrhodium(I) species, [4a, 12] we envisaged that activation of ar emote CÀHb ond by 1,4-rhodium(I) migration [12d, 13, 14] could also achieve this goal. Specifically,r hodium(I)-catalyzed reaction of an arylboron reagent with the alkyne of a1 ,3-enyne would provide the alkenylrhodium species A (Scheme 1).…”

“…Although generating electrophilic allylmetal species by allylic CÀHa ctivation is well-known, [9,10] there is,t oo ur knowledge,l imited precedent for corresponding processes that provide nucleophilic allylmetals.…”

“…[2] Theg eneration of nucleophilic allylmetal species by the activation of allylic C À Hb onds would bypass the need to prepare such reagents and potentially increase efficiencyb ys treamlining synthetic sequences.This strategy would also be avaluable complement to nucleophilic allylations involving migratory insertions of allenes, [3,4] theu se of simple p-unsaturated compounds in hydrogenative or redox-triggered additions, [5,6] hetero-ene reactions, [7] and Prins reactions. [8] Although generating electrophilic allylmetal species by allylic CÀHa ctivation is well-known, [9,10] there is,t oo ur knowledge,l imited precedent for corresponding processes that provide nucleophilic allylmetals. [11] Very recently,t he groups of Schneider, [11a] Kanai, [11b] and Mita and Sato [11c] described the formation and trapping of nucleophilic allylmetal species from simple hydrocarbons.I nv iew of the nucleophilic character of allylrhodium(I) species, [4a, 12] we envisaged that activation of ar emote CÀHb ond by 1,4-rhodium(I) migration [12d, 13, 14] could also achieve this goal.…”