Photoredox Selective Homocoupling of Propargyl Bromides

Abstract

Since the alkynyl moiety is one of the most versatile synthons for many other functional groups, 1,5-diynes (Wurtztype products of propargyl halides) would be valuable synthetic building blocks for the synthesis of complex functional molecules. However, despite the high and similar reactivity of propargyl radicals compared to allyl and benzyl derivative radicals, a photoredox Wurtz-type reaction of propargyl halides has not yet been developed. In this study, we developed the visible-light-induced selective homocoupling of propargyl bromides to form 1,5-diynes. Electrochemical and photophysical experiments showed that the key propargyl radical generation involves a reductive quenching cycle of the photoexcited [Ir(III)]* photocatalyst in the presence of N,N-dicyclohexylmethylamine. The product 1,5-diyne underwent one-step conversion to the functionalized indole derivative via Rhcatalyzed coupling with N-phenylacetamide. These results indicated the high utility of the developed homocoupling method.

Recent Advances in Visible Light Photoredox-Catalyzed Alkynylation

“…有机磷化合物是一种特殊而重要的化合物, 因其在 医药和农用化学品、有机合成以及材料科学等领域的应 用而受到广泛关注. 2018 年, 陈以昀等 [54] 利用 CIR 试 2022 年, 吴骊珠等 [57] 2022 年, Cho 课题组 [62] 报道了可见光促进炔丙基溴 化物的自偶联反应, 合成了一系列 1,5-二炔化合物 (Scheme 44). 炔丙基溴通过单电子还原得到炔丙基自 由基, 随后经过炔丙基自由基的自偶联得到产物, 反应 体系中的胺能提供电子使该反应能通过还原淬灭过程 顺利进行.…”

Photoredox-Catalyzed Redox-Neutral Decarboxylative C–H Acylations of Coumarins with α-Keto Acid

“…Compared with other acyl sources, α-keto acids have become a better choice for the synthesis of related ketone derivatives because of their low cost, stability, easy preparation, and high reactivity. − The greener characteristic of the coproduct formed in reactions using α-keto acid (only CO 2 ), together with its versatility as a building block in catalytic organic synthesis, makes it a candidate for being a green acylating agent and an alternative to acyl chloride or other acyl transfer reagents. Photoredox catalysis has been regarded as an eco-friendly and effective strategy due to its convenience, availability, and safety. − Upon irradiation with visible light, conversion of α-keto acids into acyl radicals can be achieved via a single-electron transfer (SET) process by photocatalytic oxidation and subsequent decarboxylation. − However, in most cases, an additional oxidant or additive was essential. From the perspective of green chemistry, the development of the C–H acylation reaction under oxidant and additive free conditions is highly desirable.…”

Copper-Catalyzed Asymmetric Cyanation of Propargylic Radicals via Direct Decarboxylation of Propargylic Carboxylic Acids

“…In contrast, propargylic carboxylic acids, which are easy to store and handle, have rarely been studied for decarboxylative cyanation. This may be due to the easy formation of the homocoupled byproduct . Considering the fascinating magic of the asymmetric direct decarboxylative cyanation strategy of propargylic carboxylic acids in terms of atomic economy and efficiency, we tried to achieve such a transformation with hypervalent iodine based on our previous work. , To achieve this goal, some challenges still exist: (1) as an extremely electron-deficient reagent, hypervalent iodine­(III) is susceptible to attack by a nucleophilic alkyne, even an internal alkyne, and (2) the propargylic radical formed after decarboxylation may be isomerized to an allenyl radical intermediate, which is then trapped by a chiral copper­(II) cyanide species to produce axially chiral allenyl nitrile .…”