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Spirocyclobutanes via Metal Carbene Facilitated Diastereoselective [2+2]Cycloaddition Reactions of exo-Methylene Oxacyclopentylidene Complexes of Chromium and Tungsten

✍ Scribed by Karl Heinz Dötz; Alexander W Koch; Bernd Weyershausen; Heike Hupfer; Martin Nieger

Book ID: 104202634
Publisher: Elsevier Science
Year: 2000
Tongue: French
Weight: 214 KB
Volume: 56
Category: Article
ISSN: 0040-4020
DOI: 10.1016/s0040-4020(00)00207-6

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✦ Synopsis

AbstractÐUpon reaction with enol ethers a-exo-methylene-2-oxacyclopentylidene complexes of chromium and tungsten 3 and 4 undergo [212]cycloaddition under mild thermal conditions to give spirocyclobutanes 5±12 in good yields as single diastereomers. The relative stereochemistry (as established by X-ray analysis for 9 and 10 to be 5R p ,2 H S p ) results from a combined re-si approach of both p-systems. The propensity for [212]cycloaddition depends on both the substitution pattern and the ring size of the enol ether; 1,1-disubstituted enol ethers and enamines undergo a formal conjugate addition resulting in side-chain elongation.

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