Hexa-methyldistannane

Analogously, Barrett and Kohrt transformed 2-phenyl-4-oxalone into triflate 44, which was then converted to the corresponding stannane 45 using Pd-catalyzed coupling with hexa-methyldistannane. Subsequent couphng of 45 with 2-iodooxazole provided bisoxa-zole 46 [19]. 

Palladium(0)-catalyzed intramolecular reductive coupling of the diacetates 1 and 3 with hexa-methyldistannane leads to tricyclic compounds 2 and 4, respectively, in a completely regioselec-tive manner2. Intermediate formation of a monoallyltin species followed by attack of this allyl tin moiety on the rc-allyl complex generated from the remaining allyl acetate is a likely route to the products. Since a substrate similar to 3 has been shown to isomcrizc to a nonstereogenic terminal diacetate under the conditions listed, the stereochemical results obtained for both 1 and 3 reflect the simple diastereoselectivity of these cyclizations. 

Treatment of -caprolactone with 7V,7V-bis(trimethylsilyl)lithium amide and then with A-phenyl triflimide affords 2-triflyloxy-2-hexenolide (22). The latter is obtained in 89% yield <89CL1313> and can be regarded as a key intermediate in the syntheses of diverse 2-substituted 4,5,6,7-tetra-hydrooxepines. For instance, reactions of (22) with lithium dialkyl- or diphenylcuprates result in 2-butyl-substituted derivatives (23 R = Aik, Ph) <89CL1313>, while analogous interaction with hexa-methyldistannane gives 2-trimethylstannyl-4,5,6,7-tetrahydrooxepin (23 R = SnMcj) <91SL197>. 

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