Tungsten complexes, propynyl cycloaddition reactions

The [2 + 2] cycloaddition of the propynyl tungsten complex (12b) has been found to be stereospecific with the cis and trans isomers of eAyl prc nyl ether." ITie reaction with c/s-propenyl ethyl ether gave rise to the cyclobutenyl complex (18), in addition to a minor amount of the ring-opened dienyl carbene complex (19). The stereochemistry about the double bonds in the dienyl complex (19) revealed that it was derived from a thermal electrocyclic conrotatory ring opening of the c/s-cyclobutenyl carbene complex (18) and thus the stereochemistry is completely retained in this cycloadditirxi. In support of this analysis it was found that cyclobutenyl complex (18) could be thermally opened to the dienyl complex by heating in an inert solvent at 50 C. In the cycloaddition of the propynyl complex (12) with trans-... 

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