Copper-Catalyzed Reductive Ireland–Claisen Rearrangements of Propargylic Acrylates and Allylic Allenoates

Abstract

The copper-catalyzed reductive Ireland–Claisen rearrangement of propargylic acrylates led to 3,4-allenoic acids. The use of silanes or pinacolborane as stoichiometric reducing agents and triethylphosphite as a ligand facilitated the divergent and complementary selectivity for the synthesis of diastereomeric anti- and syn-rearranged products, respectively. Copper-catalyzed reductive Ireland–Claisen rearrangement of allylic 2,3-allenoates proceeded effectively only when pinacolborane was used as a reductant to generate various 1,5-dienes in excellent yields and with good diastereoselectivities in some cases. Mechanistic studies showed that the silyl and boron enolates, rather than the copper enolate, underwent a stereospecific rearrangement via a chairlike transition state to afford the corresponding Claisen rearrangement products.

Recent Advances in Catalytic [3,3]-Sigmatropic Rearrangements

“…In 2021, copper-catalyzed reductive Ireland-Claisen rearrangements were expanded to propargylic acrylates 10 and allylic allenoates 13 (Scheme 3) [23]. Silane and borane were used as reductants, and the substrates 10 and 13 were, respectively converted into the silyl and boron enolates 11 and 14 via the in situ conjugated reduction by a copper hydride catalyst.…”

“…Electrophilic ketenimine 22 was converted into propargyl vinyl ether 23 by the nucleophilic addition of propargyl alcohol 16, and the Claisen rearrangement ensued to form an allenic amide 19. Isomerization of allene 19 into the propargyl group 18 proceeded via 1,3-hydrogen transfer, which may be promoted by the In 2021, copper-catalyzed reductive Ireland-Claisen rearrangements were expanded to propargylic acrylates 10 and allylic allenoates 13 (Scheme 3) [23]. Silane and borane were used as reductants, and the substrates 10 and 13 were, respectively converted into the silyl and boron enolates 11 and 14 via the in situ conjugated reduction by a copper hydride catalyst.…”