Alkene Metathesis Synthesis of Kainic Acid, Pladienolide B and Amphidinolide

The second alkene metathesis step was the coupling of 12 with 13. The most effective catalyst in this case was the second generation Grubbs. Note that the free alcohol 13 participated successfully in the cross-coupling. According to the authors, this is one of just a few examples of successful cross coupling of an alkene adjacent to a quaternary center. 

Selvakumar of Dr. Reddy s Laboratories, Ltd., Hyderabad approached (reira/iedron Lett. 2007,48, 2021) the synthesis of phaseolinic acid 6, there was some concern about the projected cyclization of 2 to 3, as this would involve the coupling of two electron-deficient alkenes. In fact, the Ru-mediated ring-closing metathesis proceeded efficiently. The product unsaturated lactone 3 could be reduced selectively to either the trans product 4 or the cis product 5. 

There has been relatively little work on the s nithesis of the higher branched sugars, such as the octalose 13, a component of several natural products. The synthesis of 13 Organic Lett. 2007, 9, 4777) by Ulrich Koert of the Philipps-University Marburg also began with a Baylis-Hilhnan product, the easily-resolved secondary alcohol 8. As had been observed in other contexts, cyclization of the protected allylic alcohol 9a failed, but cyclization of the 

Intramolecular alkyne metathesis is now well-established as a robust and useful method for organic S5mthesis. It was also known that Ru-mediated metathesis of an alkyne with ethylene could lead to the diene. The question facing Angew. Chem. Int. Ed. 2007, 46, 5545) Alois Fiirstner of the Max-Planck-Institut, Mulheim was whether these transformations could be carried out on the very deUcate epoxy alkene 21. In fact, the transformations of 21 to 22 and of 22 to 23 proceeded weU, setting the stage for the total synthesis of Amphidinolide V 25. 

Alkene metathesis has been used to prepare more and more challenging natural products. The first and second generation Grubbs catalysts 1 and 2 and the Hoveyda catalyst 3 are the most widely used. 

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Alkene Metathesis Synthesis of Kainic Acid, Pladienolide B and Amphidinolide Y... 

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