Since C-H bond is the basic unit of organic compounds, it's considered to be a concise synthesis method to implement direct functionalization of C-H bond. As carboxylic acids are widely found in nature, carboxyl group can act as both directing group and leaving group to drive transition metal-catalyzed controllable transformation of ortho-C-H bond functionalization of carboxylic acid that not only avoids the extra introduction and removal of the directing group in the process of C-H bond activation, but also highlights the simplicity of C-H bond activation and green of decarboxylation with "one stone and two birds" strategy of the carboxyl group. Therefore, basing on the strategy of "two birds with one stone", ortho-C-H bond functionalization of carboxylic acid using carboxyl as a traceless directing group can provide a new strategy and method for controllable and directional synthesis, which has considerable significance in synthetic chemistry. According to the types of coupling partners involved in the transformations, transition metal-catalyzed ortho-C-H bond activations of carboxylic acids with multiple-bond-containing reagents, arylating compounds and heteroatom-containing chemicals are reviewed respectively based on the strategy of "two birds with one stone", and the relevant reaction mechanisms are discussed.
In this study, we introduce a new literature-aging conceptual model (Bailón-Moreno, 2005) to study citation curve and to discuss its implications. First, we improve the conceptual model by adding a period to describe the "death" of citations. Second, we offer a feasible operationalization for this conceptual model and implement a set of cross-discipline publications in the Web of Science to test its performance. Furthermore, we propose two measurements according to the new model-SP and RP-to capture the patterns of citation curve of publications. For example, we find that half papers in Arts & Humanities published in 1985 almost receive no or extremely few citations in the first five years after their publication; on average, those papers in Arts & Humanities have a five-years-long period when their citations grow rapidly. In addition, we observe a special phenomenon named "literature revival" as some publications may have multiple citation life cycles, which received little attention from current researches. Finally, we discuss the implications of our study, especially the application of the SP and RP in improving scientific evaluation and collection development in library, and the inspiration of "literature revival".
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