Nine-membered rings synthesis

The precatalyst loading was high (10—20%), and only 58% conversion was achieved after three days in toluene at room temperature. However, this represents one of the few successful non-annelative cyclononene syntheses by RCM in the Hterature. Other examples of nine-membered ring synthesis have typically involved annelation rather than annulation. " " " ... 

When K.yba, Cram and coworkers attempted the synthesis of dibinaphthyl-22-crown-6 from binaphthol and diethylene glycol ditosylate. the reagent ratio was as described either by V or X (Eqs. 3.1 or 3.3). The intent was to make the 22-membered ring. Some of the 11-membered ring was isolated as well (Eq. 3.5). None was apparently observed for the benzo case because the nine-membered ring is less favorable. In short, it is not the intent of the synthesis but the reaction dynamics which determine the product. 

Scheme 34 Formation of the central nine-membered ring and completion of the carbon skeleton in Hirama s improved total synthesis of the marine neurotoxin ciguatoxin CTX3C (183)[90b]...

The reaction in Entry 8 was used in the synthesis of members of the phomoidrides. The cyclohexene ring that is constructed creates a bicyclo[4.3.1]skeleton containing seven- and nine-membered rings. 

Molander, G. A. Kollner, C. Development of a protocol for eight- and nine-membered ring 488 synthesis in the annulation of sp2,sp3-hybrid-ized organic dihalides with keto esters. /. Org. Chem. 2000, 65, 8333-8339. 

There has been a tremendous increase in the methodology available to assemble nine-membered ring systems during the last decade. Development of efficient routes to prepare various natural products was a primary goal of numerous studies. Synthesis of different saturated structures relative to crown ethers, usually with 1,4,7-heteroatom pattern, were of great importance. 

Novel stereocontrolled synthesis of the nonacene ring system ofbrevetoxin A. Conformationai-reactivity effects in nine-membered rings... 

K., Synthesis of retinals with eight- and nine-membered rings in the side chain. Models for rhodopsin photobleaching intermediates. J. Org. Chem., 58, 3533, 1993. 

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