The asymmetric phospha-Michael addition of dialkyl phosphite to α,β-unsaturated carbonyl compounds by using an azetidine-derived dinuclear zinc catalyst was described. The catalyst was proved to be general and efficient for a broad spectrum of enones and α,β-unsaturated N-acylpyrroles. A series of phosphonate-containing compounds were generated with excellent enantioselectivities (up to 99% ee) and chemical yields (up to 99%) under mild conditions without using additives. The products were obtained with more than 95% ee for 23 examples of α,β-unsaturated carbonyl compounds. A positive nonlinear effect was observed and the possible mechanism was proposed.
Apratoxin
A is a potent anticancer natural product whose
key polyketide
fragment constitutes a considerable challenge for organic synthesis,
with five prior syntheses requiring 12 to 20 steps for its preparation.
By combining different redox-economical catalytic stereoselective
transformations, the key polyketide fragment could be rapidly prepared.
Followed by a site-selective protection of the diol, this strategy
enables the preparation of the apratoxin A fragment in only six steps,
representing the shortest route to this polyketide.
The enantioselective construction of fluorohydrins featuring a tetrasubstituted stereocenter embedded in complex frameworks represents an important challenge. Herein, we report a multicatalytic strategy enabling the stereoselective preparation of a new type of scaffold containing such a challenging fluorohydrin motif. The sequence is based on an organocatalyzed fluorination of α‐disubstituted aldehydes followed by a diastereoselective copper‐catalyzed decarboxylative aldol reaction. Reduction of the generated β‐hydroxy ketone followed by a Lewis base‐catalyzed kinetic resolution enables the isolation of original fluorinated 1,3‐diols with perfect diastereo‐ and enantio‐control.
In order to prepare more efficiently key 1,3-diol fragments, we have devised a base-promoted redox-neutral condensation of ketones with alcohols. This diastereoselective alcohol−aldolization enables bypassing the classical oxidation and reduction steps necessary for the preparation of this crucial backbone by an overall redox-neutral formal borrowing hydrogen process. The starting alcohols constitute both the precursors of the in situ generated reactive aldehydes and the hydride source necessary for the chemoselective reduction of the aldol adduct intermediates.
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