Enantioselective Synthesis of β-Allenoates via Phosphine-Catalyzed and ZnI₂-Promoted Preparation of Oxazolidines and Propargylamines Using Chiral Amines, 1-Alkynes, and Propiolates

Abstract

Diphenylphosphinoethane (DPPE)-catalyzed and ZnI-promoted in situ formation of oxazolidine, alkynyl zinc, and propargylamine intermediates from 1-alkynes, chiral (S)-diphenyl(pyrrolidin-2-yl)methanol, and propiolates gave the corresponding chiral (R)-β-allenoates in 40-72% yield with up to >99% ee. The intermediate propargylamine was isolated in 50% yield and converted to give the β-allenoate 10aa in 68% yield and 96% ee upon reaction with ZnI. The results are discussed considering a mechanism involving oxazolidine and iminium ions formed in situ followed by addition of alkynyl zinc complex to produce the propargylamine that gives the corresponding allenoate via a 1,5-hydrogen shift in the presence of ZnI.

Synthesis of Propargylamines via Michael Addition Using Methyl Vinyl Ketone Derivatives, 1-Alkynes, and Secondary Amines Catalyzed by Copper (I) Halides

“…Recently, convenient methods have been developed to access chiral propargylamines and chiral allenes via CuX- and ZnX 2 -promoted transformations. , In continuation of these studies, we have explored the synthesis of propargylamines via the Michael addition using readily available methyl vinyl ketone, morpholine, and phenyl acetylene with different metal salts like ZnCl 2 , ZnBr 2 , ZnI 2 , CuCl, CuBr, and CuI in various solvents (Table ).…”

“…Over the years, several synthetic methods were developed using aldehydes (or) ketones, 1-alkynes, and amines to access propargylamines. − In continuation of the studies on the synthesis of propargylamines and their conversion to allenes in this laboratory, , we wish to report herein an unprecedented copper-catalyzed reaction using methyl vinyl ketone derivatives, 1-alkynes, and secondary amines to access di-, tri-, and tetrasubstituted propargylamines.…”

Alkyl amines and ethers as traceless hydride donors in [1,5]-hydride transfer cascade reactions

“…Considering that the crucial [1,5]-HT step of propargylic amines can be promoted by diverse metals, including [Cu], 7,9–21 [Zn], 22–33 [Au], 34–36 [Ag], 37 [Cd], 38–40 and [Pd], 41–45 we would like to divide the representative examples, for clarity, into six parts that apply different metal promoters.…”

“…In particular, Ma's group have made great contributions, and in 2019 they published an account that described their efforts toward the development of ATA reactions. 8 Considering that the crucial [1,5]-HT step of propargylic amines can be promoted by diverse metals, including [Cu], 7,9-21 [Zn], [22][23][24][25][26][27][28][29][30][31][32][33] [Au], [34][35][36] [Ag], 37 [Cd], [38][39][40] and [Pd], [41][42][43][44][45] we would like to divide the representative examples, for clarity, into six parts that apply different metal promoters.…”

Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth Metal Complexes Containing Trost Ligands

“…The design and preparation of chiral ligands are critical. During the last decades, prolinol and its derivatives were proven to be a kind of efficient chiral ligands, which were used in asymmetric alkyne addition, transfer hydrogenation, epoxidation, and Henry condensation (Figure a). Meanwhile, a series of chiral phenoxy-functionalized prolinolates were developed and successfully employed in asymmetric Michael addition, epoxidation, hydrophosphonylation, and hydroboration (Figure b).…”