Calcium aryloxides

A variant of direct metallation, cocondensation, has been utilized to prepare the first <7-bonded organocalcium complex, (SiMe3)2CH 2Ca(l,4dioxane)2, in addition to a transient heteroleptic calcium hydride, CeHsCaH by C-H activation (equation 3). The heteroleptic hydride is highly reactive and decomposes upon warming the reaction vessel above —78 °C. The product has been identified by its reaction with alcohols, affording quantitatively a series of calcium aryloxides. 

Ikegami et al. reported an asymmetric Morita—Baylis—HUlman reaction using a BlNOL-calcium complex as a chiral Lewis acid and tributylphosphine as an achiral Lewis base (Scheme 2) [24]. It was found that an active calcium aryloxide catalyst could be prepared from Ca(0 Pr)2 and (f )-BINOL in THF. The reaction of cyclopentenone with 3-phenylpropionaldehyde was tested in the presence of the calcium complex, and the desired Morita-Bayhs-Hillman adduct was obtained in 62 % yield with 56 % ee. 

Recently (33, 59), soluble monomeric alkoxides (aryloxides) of calcium and barium have been synthesized by the reactions of their iodides with the potassium salts of sterically hindered alcohols (phenols). 

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