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The secret weapon of cascade reaction: How to complete complex synthesis in one reaction?
In the field of chemistry, cascade reactions, also known as multiple or series reactions, have attracted increasing attention due to their unique characteristics. This reaction process involves at least two consecutive reactions, and the production of each subsequent reaction must rely on the chemical functionality produced in the previous step. This property enables cascade reactions to generate complex compounds all at once without the need to isolate intermediates individually, saving time and resources.
The main advantages of cascade reactions include high atom economy and reduced waste generation during chemical processes, making them an important component of green chemistry.
The importance of cascade reactions in the field of total synthesis has been apparent since Robinson reported the synthesis of solanol in 1917. With the advancement of science and technology, the development of this methodology has grown rapidly, especially in the application of asymmetric catalysis. The development of cascade processes using chiral organic catalysts or transition metal complexes has also become a new research topic. focus.
Nuclear electrophilic cascade reaction
The nuclear electrophilic cascade reaction is believed to be one of the easiest reactions to understand. The key steps of such reactions usually involve nucleophilic or electrophilic attack. For example, in the synthesis of the broad-spectrum antibiotic (-)-chloramphenicol reported by Raos et al., the synthesis of the compound was completed through a series of nucleophilic attack reactions.
The data showed that an overall yield of 71% was obtained, which is quite impressive in a multi-step chemical synthesis.
Organocatalytic cascade reactions
Organocatalytic cascade reactions are a subclass in which nucleophilic attack is driven by an organic catalyst. For example, the synthesis of the natural product Harziphilone reported by Sorensen et al. in 2004 was carried out using an organic catalyst and the reaction was completed efficiently.
Free Radical Cascade Reaction
Free radical-based cascade reactions are more efficient due to the high reactivity of free radical species and are often used to synthesize complex compounds, such as in the synthesis of (±)-Hirsutene made in 1985. . This provides a new direction for the application of cascade reactions.
Cyclic cascade reaction
Periodic reactions are the most common type of cascade processes and include cycloadditions, electrocyclic reactions, and σ-translocations. For example, the synthesis of Endiandric Acid reported by Nicolaou, in which multiple electrocyclic reactions transformed into each other and finally formed the target product, demonstrated a synthetic pathway with color, aroma and taste.
Transition metal catalyzed cascade reactions
Transition metal-catalyzed cascade reactions combine the innovation of organometallic chemistry with the economy of cascade reactions, becoming one of the green technologies in organic synthesis. Cascade reactions catalyzed by Rh can efficiently transform different compounds, demonstrating its great potential in contemporary chemistry.
The research shows that these reactions are not only environmentally friendly but also demonstrate efficient synthetic pathways.
In summary, cascade reactions provide an efficient strategy for chemical synthesis, and are an indispensable tool especially for the total synthesis of natural products. In the future, how can we further optimize and develop these reactions to meet the growing demand for synthesis and environmental protection? This is a question worth pondering.
