A form independent activation of zinc, concomitant generation of organozinc species and engagement in a Negishi cross‐coupling reaction via mechanochemical methods is reported. The reported method exhibits a broad substrate scope for both C(sp3)–C(sp2) and C(sp2)–C(sp2) couplings and is tolerant to many important functional groups. The method may offer broad reaching opportunities for the in situ generation organometallic compounds from base metals and their concomitant engagement in synthetic reactions via mechanochemical methods.
A general method for the synthesis
of secondary homoallylic alcohols
containing α-quaternary carbon stereogenic centers in high diastereo-
and enantioselectivity (up to >20:1 dr and >99:1 er) is disclosed.
Transformations employ readily accessible aldehydes, allylic diboronates,
and a chiral copper catalyst and proceed by γ-addition of in
situ generated enantioenriched boron-stabilized allylic copper nucleophiles.
The catalytic protocol is general for a wide variety of aldehydes
as well as a variety of 1,1-allylic diboronic esters. Hammett studies
disclose that diastereoselectivity of the reaction is correlated to
the electronic nature of the aldehyde, with dr increasing as aldehydes
become more electron poor.
A form independent activation of zinc, concomitant generation of organozinc species and engagement in a Negishi cross‐coupling reaction via mechanochemical methods is reported. The reported method exhibits a broad substrate scope for both C(sp3)–C(sp2) and C(sp2)–C(sp2) couplings and is tolerant to many important functional groups. The method may offer broad reaching opportunities for the in situ generation organometallic compounds from base metals and their concomitant engagement in synthetic reactions via mechanochemical methods.
A practical method for the efficient and enantioselective preparation of versatile ketones and aldehydes that contain an α-quaternary stereocenter is described. Reactions utilize simple carboxylic acid or ester starting materials, a monodentate chiral phosphine, and afford a variety of aryl, alkenyl, alkynyl, and alkylsubstituted ketone and aldehyde products in 25-94 % yield and 90 : 10 to > 99 : 1 enantiomeric ratio. Reactions proceed by acyl substitution with in situ formed chiral allylic nucleophiles, and display selectivity and conversion dependence on a protic additive. The utility of the approach is demonstrated through several product transformations.
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