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46.3.3.1 Variation 1: Metathesis of Alkynes with Ethene

DOI: 10.1055/sos-SD-046-00046

Diver, S. T.Science of Synthesis, (200946121.

The cross enyne metathesis between alkynes and ethene is an effective way to synthesize substituted buta-1,3-dienes. Using an atmosphere of ethene gas supplied through a balloon, an effective cross metathesis with a variety of terminal and internal alkynes has been demonstrated[‌25‌] (see also Section 46.3.1.1). These early studies utilized the first-generation Grubbs catalyst 1 (see Scheme 3) and required extended reaction times. The procedure produces 2-substituted buta-1,3-dienes from terminal alkynes and 2,3-disubstituted buta-1,3-dienes from internal alkynes (Scheme 37). The cross metathesis has seen many more examples of terminal alkyne reactions than that of internal alkynes, although each class of alkyne appears to be reactive. Even though the intramolecular ring-closing metathesis with Grubbs carbenes demonstrates excellent functional-group tolerance, intermolecular reactions are more demanding. In general, cross-metathesis reactions are more sensitive to functional groups, particularly strongly coordinating groups such as alkyl ethers. If the heteroatom functionality is more remote or if the Lewis basic nature of the heteroatom is attenuated, then the reaction is fairly reliable. Nonetheless, the nature of the bimolecular reaction reveals some limitations for certain substrates, thought to arise from chelate stabilization of reactive intermediates.

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