The cover picture, provided by Fandrick, Fandrick, and Senanayake, depicts the copper-catalyzed asymmetric propargylation of aldehydes. The process is based on a copper alkoxide-promoted B/Cu exchange to generate an allenyl copper intermediate. The process is initiated by ligand exchange of the ligated copper(II) isobutyrate complex with lithium tert-butoxide, wherein the resulting copper alkoxide complex undergoes an exchange with the propargyl borolane reagent to generate the key allenyl copper intermediate. After propargylation of an aldehyde, the resulting homopropargylic alkoxide copper complex readily participates in another B/Cu exchange to complete the catalytic cycle. Employing the MeOBIBOP ligand allows for exceptional control of both enantioselectivity and site selectivity for the homopropargylic alcohol. This two-step process, wherein the product of the alkylation readily reacts with a stoichiometric reagent to regenerate the active nucleophile provides an operationally simple process to effect the propargylation of aldehydes with broad functional group tolerance.
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