Rhodium-Catalyzed Asymmetric Conjugate Alkynylation of β,γ-Unsaturated α-Ketoesters

Abstract

The first example of catalytic asymmetric conjugate alkynylation of β,γ-unsaturated α-ketoesters is reported. By using Rh(I)/(R)-DM-binap complex as the catalyst and diphenyl[(triisopropylsilyl)ethynyl]methanol as the alkynylating reagent, the alkynylation reaction proceeded smoothly to afford α-ketoesters bearing a propargylic chiral center at γ position in good yields with high enantioselectivities.

Rhodium(I)‐Catalyzed Arylation/Dehydroxylation of tert‐Propargylic Alcohols Leading to Tetrasubstituted Allenes

“…Thus, introduction of an efficient method for the synthesis of diverse tetrasubstituted allenes is still highly desired. As part of our ongoing efforts on the Rh(I)‐catalyzed transformations of tert ‐propargylic alcohols, we investigated the Rh(I)‐catalyzed arylative transformations of those substrates. Herein, we report our finding that the Rh(I)‐catalyzed reactions of readily available tert ‐propargylic alcohols and arylboroxines could provide a versatile approach to the synthesis of diverse tetrasubstituted allenes (Scheme ).…”

“…As exemplified in Scheme , the use of tert ‐propargylic alcohols under Rh(I)‐catalyzed arylation conditions can pose big challenges to the study. First, the tert ‐propargylic alcohol is known to undergo β‐alkynyl elimination in the presence of a rhodium(I) catalyst,, which would lead to the dimerization or decomposition of 1 a . Second, the Meyer−Schuster rearrangement of the tert ‐propargylic alcohol (i. e., 1 a to 5 a ) can be a major side reaction since both Lewis acidic transition‐metals and arylboronic acids are known to catalyze this transformation .…”

Palladium-catalyzed intermolecular alkynylcarbonylation of unactivated alkenes: easy access to β-alkynylcarboxylic esters

“…3 Recently, transition metal-catalyzed conjugate additions with alkynes as nucleophiles have also been documented (Scheme 1a). 4,5 Owing to the easy availability of unactivated alkenes, the direct alkynylation of unactivated terminal alkenes is more attractive, but rare examples have been documented to date. 6,7 Herein, we communicate a palladium-catalyzed alkynylcarbonylation of unactivated alkenes with ethynyl benziodoxolone (EBX) reagents under mild conditions, which provides an efficient method for the synthesis of β-alkynylcarboxylic esters (Scheme 1b).…”

Progress in Cyclizations of 4‐Acetylenic Ketones: Synthesis of Furans and Pyrroles

“…In addition to the commonly methods mentioned above, other methods were also reported (Scheme 9), for example: (a) alkynylation of α,β-unsaturated ketones 38, [21,22] (b) reaction of enamine 40 with propargyl bromide 41, [21,22] (c) step-wise synthesis starting with methyl 6-oxohex-2-ynoate 42, [23] (d) asymmetric conjugate addition of 1,3-dicarbonyl compounds 1 to nitroenynes 43, [24] (e) ZnCl 2 -TMSCl-catalyzed cross-coupling reaction of acetyl acetone 45 with propargyl sulfonamide 44, [25] (f) p-TSA⋅H 2 O catalyzed reaction of α-oxoketene-N,S-acetals 46 with propargyl alcohols 47, [26] (g) nitrosative degradation of the isoxazol-5-ones 48, [27] (h) Rhodium-catalyzed asymmetric conjugate alkynylation of β,γ-unsaturated α-ketoesters 49. [28] Diverse 4-acetylenic ketones with crucial, useful and complex functional groups were synthesized followed by above synthetic strategies, which supported strongly for the next application and development of synthesis methodology based on 4-acetylenic ketones.…”