钯催化吲哚直接羰化合成吲哚-3-炔酮类化合物

Palladium‐catalyzed synthesis of indole‐3‐alkynones via direct carbonylation of indoles

以Pd(OAc)2为主催化剂,以Cu为助催化剂,以碘为氧化剂,高效地实现了吲哚与苯炔直接羰化合成吲哚-3-炔酮,并优化了反应条件. 结果表明,该催化剂体系对带有不同取代基的吲哚、端炔类化合物具有非常好的适用性,最高分离产率可达94%. 生成的吲哚-3-炔酮产物可进一步与叠氮化钠和溴苄一锅反应,高产率地得到3-甲酰三唑基吲哚类化合物. 由于原料来源简单,产率高,且两类产物都是重要的中间体,因此该方法具有一定的应用价值.

A new method has been developed for the Pd‐catalyzed direct carbonylation of indoles with phenylacetylenes.The process involved the initial iodination of the indole to afford the corresponding 3‐iodo‐indole,which was subsequently carbonylated with a variety of different alkynes using Pd（0） to yield the indole‐3‐alkynones.In contrast to the traditional Pd‐catalyzed oxidative carbonylation strategy,which involves the Pd（II）‐mediated activation of the aromatic C-H bonds,the aromatic CH bonds in the current process were activated by iodine oxidation,eliminating the problems associated with the reduction of Pd（II） to Pd（0） under the CO atmosphere.Following an extensive screening process,Pd（OAc）2/CuI was identified as the most efficient catalyst system for the reaction in the presence of a base and iodine as an oxidant under mild conditions（0.2 MPa CO,90°C）.The reaction provided the desired products in moderate to excellent isolated yields（up to 94%） and good tolerance to a variety of different functional groups.The structure of a representative alkynone product（3he） was unambiguously verified by X‐ray single crystal structure analysis.Furthermore,the carbonylation products underwent a three‐component reaction with sodium azide and benzyl bromide to give the corresponding 1,2,3‐triazole analogues in the absence of any catalyst,thus expanding the synthetic application of the current methodology.