O-Heterocyclic Construction by Alkene Metathesis

Kevin J. Quinn of the College of the Holy Cross chose (Organic Lett. 2005, 7, 1243) a complementary approach in his synthesis of rollicosin. The symmetrical diol 4 is also available from carbohydrate precursors. Monosilylation followed by esterification with acryloyl chloride gave 5. Exposure of 5 to the Grubbs catalyst in the presence of 6 led, by ring-closing metathesis and cross metathesis, to the y-lactone 7. Note that 5-lactone formation did not compete  

Stereodefined spiroketals are a common structural motif in physiologically-active natural products. Richard P, Hsung of the University of Minnesota lecently nsported Organic Lett. 2005, 7, 2273) that TfjNH is a particulary effective Brdnsted acid mediator for the stereoselective coupling of vinyl lactols such as 11 with homoallylic acids such as 12. The axial ethers so produced undergo smooth ringclosing metathesis to the spiroketals. 

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