A series of ruthenium catalysts has been screened in the self-metathesis of 1-dodecene with and without the addition of benzoquinones. Many of these catalysts demonstrated excellent selectivity and yields with as low as 10 ppm catalyst loading. Reactions have been conducted under decreased pressure or under argon bubbling, which caused a tremendous increase in yield and selectivity of the examined process.Scheme 1. Possible reactions of linear alkenes in the presence of metathesis catalyst (PMP = primary metathesis products, IP = isomerization products, SMP = secondary metathesis products).Scheme 2. Self-metathesis of 1-dodecene. 1998
To extend the versatility of the ruthenium carbene-promoted enyne metathesis, it was combined with an Ireland ester enolate Claisen rearrangement. This reaction sequence provided conjugated dienes of higher substitution pattern than that obtained through a cross-enyne metathesis alone. The Ireland-Claisen was conducted across both acyclic and cyclic dienes produced from cross-metathesis and methylene-free enyne metathesis, respectively. In the case of cyclodienes, the Ireland-Claisen rearrangement produced s-trans locked dienes which underwent mode-selective ene reaction. The tandem, sequential use of the Ireland-Claisen rearrangement also proved suitable for chirality transfer originating from chiral propargylic alcohols. Last, the tandem metathesis/Ireland-Claisen was utilized to access 4-substituted-3,5-cyclohexadiene diol derivatives, which are valuable chiral intermediates for natural product synthesis. The combination of this pericyclic reaction with a catalytic metathesis reaction extends the versatility of cross-metathesis since additional diene motifs can be accessed.
A general synthetic approach towards a class of water-soluble, high quantum yield fluorescent saccharide reporters using 6-morpholinonaphthalene-2-yl boronic acid as an illustrative case is reported. The strength and flexibility of this approach, which utilizes the Buchwald–Hartwig cross-coupling reaction, is further underscored by the preparation of several additional aminonaphthalenes in excellent yield, including one that bears a chiral unit.
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