Cross-coupling reactions precursor reactivity

Ruthenium catalyst 6 enables the cycloaddition of iododiynes while preserving the reactive carbon-iodine bonds hence, the resulting iodoarenes can be applied to further cross-coupling reactions [49], Yamamoto et al. exploited ruthenium-catalyzed [2 + 2 + 2] cycloaddition for the construction of an interesting spirocyclic C-arylglycoside motif, which is found in bioactive natural products (i.e., papula-candins) (Scheme 3.29). In this study, idododiyne precursor 145 was prepared and... 

Retrosynthetically, spiroketal precursor 8 would be accessed via a diaster-eoselective aldol reaction between chiral aldehyde 9 and a-chiral (3-arylated methyl ketone 10 (Scheme 3). Aldehyde 9 would be readily accessible from commercially available ethyl (S)-hydroxybutyrate, while methyl ketone 10 would be constmcted by the Suzuki cross-coupling of trifluoroboratoamide 11 and rotationally symmetric aryl halides 12/13. The use of Br or I in place of Cl in halides 12/13 was intended to increase the reactivity of 12/13 toward oxidative insertion and overcome the steric hindrance imparted by the ortho-disubstituted aromatic framework. The required functionalization of the aromatic ring to install the phthalide motif was envisioned to be possible via iridium-catalyzed CH-borylation either before or after formation of the spiroketal core. Our group already had experience with this remarkable transformation in the context of naphthalene chemistry. 

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