Qiu Zihang, Li Chao-Jun
Department of Chemistry and FQRNT Centre for Green Chemistry and Catalysis, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada.
Chem Rev. 2020 Sep 23;120(18):10454-10515. doi: 10.1021/acs.chemrev.0c00088. Epub 2020 Aug 28.
Employing phenols and phenol derivatives as electrophiles for cross-coupling reactions has numerous advantages over commonly used aryl halides in terms of environmental-friendliness and sustainability. In the early stage of discovering such transformations, most efforts have been devoted to utilizing highly activated sulfonate types of phenol derivatives (e.g., OTf, OTs, etc.), which have similar reactivities to the corresponding aryl halides. However, a continuing scientific challenge is how to achieve the direct C-O functionalizations of relatively less-activated phenol derivatives more efficiently. In this review, we will focus on the recent updates on the C-O functionalizations of less-activated phenol derivatives, from aryl carboxylates (e.g., pivalates, acetates, etc.), aryl carbamates and carbonates, to aryl ethers (anisoles, diaryl ethers, aryl pyridyl ethers, aryl silyl ethers), to phenolate salts, and ultimately to simply unprotected phenols, sorted by the types of bond formations. Both transition-metal-catalyzed and transition-metal-free protocols will be covered and discussed in detail. Instead, the C-O functionalizations of aryl sulfonates will not be covered extensively unless they are closely related, due to their high reactivity. Since aryl ethers and phenols represent the main linkages or units in lignin biomass, the successes of such transformations will potentially make major contributions to the direct lignin biomass upgrading and depolymerization.
与常用的芳基卤化物相比，使用酚类和酚衍生物作为亲电试剂进行交叉偶联反应在环境友好性和可持续性方面具有诸多优势。在发现此类转化的早期阶段，大多数努力都致力于利用高活性的磺酸酯类酚衍生物（例如，OTf、OTs等），它们具有与相应芳基卤化物相似的反应活性。然而，一个持续存在的科学挑战是如何更有效地实现相对活性较低的酚衍生物的直接C-O官能化。在这篇综述中，我们将重点关注活性较低的酚衍生物的C-O官能化的最新进展，从芳基羧酸盐（例如，新戊酸酯、乙酸酯等）、芳基氨基甲酸盐和碳酸酯，到芳基醚（苯甲醚、二芳基醚、芳基吡啶醚、芳基硅醚），再到酚盐，最终到简单的未保护酚，按照键形成类型进行分类。过渡金属催化和无过渡金属的反应方案都将涵盖并详细讨论。相反，芳基磺酸盐的C-O官能化除非密切相关否则不会广泛涉及，因为它们具有高反应活性。由于芳基醚和酚是木质素生物质中的主要连接键或单元，此类转化的成功将有可能对木质素生物质的直接升级和降解做出重大贡献。
