Annulation

About: Annulation is a research topic. Over the lifetime, 10152 publications have been published within this topic receiving 189701 citations.

Rhenium-Catalyzed Synthesis of 3-Imino-1-isoindolinones by CH Bond Activation: Application to the Synthesis of Polyimide Derivatives**

Abstract: Polyimides, rigid polymers with high strength intensity, heatresistance properties, and electric nonconductance, are useful and important in the fields of aerospace engineering [1] and electronic materials. [2] Polyimides have low solubility in organic solvents, thus making it difficult to fabricate them into the desired shapes. We considered that the low solubility could be improved by changing the carbonyl group (C=O) of the polyimides into an imino group (C=N) with a long alkyl chain on the nitrogen atom. Polyimides are usually synthesized by polycondensation of pyromellitic dianhydride and diamines, [3] and thus it is difficult to synthesize imino-groupcontaining polyimides using a standard polyimide synthesis. Because CH bond transformations are highly efficient and generate only small amounts of waste, we developed a CH bond transformation which could be applied to the synthesis of such polymers. Although several studies have reported the synthesis of polymers by CH bond activation, such as CH/olefin coupling (Figure 1 a) [4] and CH/CX biaryl coupling (Figure 1 b), [5] there are no examples of polymer synthesis by annulation through CH bond activation. Our group [6] as well as others [7] previously reported transition-metal-catalyzed annulation reactions through CH bond activation by using an imino group as a directing group. In these reactions, however, the functional groups (directing groups) do not remain in the products. To maintain the functional group, we designed a method to introduce a leaving group to the directing group of a substrate (methoxy groups in Figure 1 c). With this strategy, we expected that the C=N double bonds of the imino groups would be restored by elimination of the leaving groups after intramolecular nucleophilic cyclization. Our retrosynthetic strategy is shown in Figure 2: 1) the final product (3-imino-1-isoindolinone) is produced by the elimination of methanol from the intermediate A ,2 )A is

Anodic amide oxidations: total syntheses of (-)-A58365A and (.+-.)-A58365B

Abstract: An anodic amide oxidation-iminium ion cyclization strategy for annulating rings onto amines and amino acid derivatives has been used to synthesize the angiotensin-converting enzyme inhibitors (-)-A58365A and (±)-A58365B. Both syntheses take advantage of the ability of electrochemistry to selectively oxidize an amide in the presence of a disubstituted acetylene nucleophile. In the synthesis of A58365A, an electrolysis substrate (10) derived from proline was oxidized using constant current electrolysis conditions, an undivided cell, a carbon anode, and a 0.03 M tetraethylammonium tosylate in methanol electrolyte solution. An 83% isolated yield of the N-α-methoxyalkyl amide product 11 was obtained. The annulation procedure and formation of the desired 1-aza-2,5-dioxobicyclo[4.3.0]nonane ring skeleton were completed by treatment of the methoxylated amide with titanium tetrachloride followed by ozonolysis of the resulting vinyl chloride product. Keto amide 14 was obtained from this sequence in an 83% yield (69%) over the three steps starting from the electrolysis precursor). In the synthesis of A58365B, a naerly identical procedure was used to convert an electrolysis substrate (25) derived from pipecolic acid into the required 1-aza-2,5-dioxobicyclo[4.4.0]decane ring skeleton. In this case, the overall yield of the three-step procedure was 74%. The success of these two annulation procedures serves to highlight the utility of anodic amide-oxidation-based annulation procedures for constructing bicyclic lactam enzyme inhibitors

Palladium/Norbornene-Catalyzed Indenone Synthesis from Simple Aryl Iodides: Concise Syntheses of Pauciflorol F and Acredinone A.

Abstract: To show the synthetic utility of palladium/norbornene (Pd/NBE) cooperative catalysis, here we report concise syntheses of indenone-based natural products, pauciflorol F and acredinone A, which are enabled by direct annulation between aryl iodides and unsaturated carboxylic acid anhydrides. Compared to the previous indenone-preparation approaches, this method allows simple aryl iodides to be used as substrates with complete control of the regioselectivity. The total synthesis of acredinone A features two different Pd/NBE-catalyzed ortho acylation reactions for constructing penta-substituted arene cores, including the development of a new ortho acylation/ipso borylation.