CuI/Pd0 cooperative dual catalysis: Tunable stereoselective construction of tetra-substituted alkenes
This paper describes a tunable and stereoselective dual catalytic system that uses copper and palladium reagents. This cooperative silylcupration and palladium-catalyzed allylation readily affords trisubstituted alkenylsilanes. Fine-tuning the reaction conditions allows selective access to one stereoisomer over the other. This new methodology tolerates different substituents on both coupling partners with high levels of stereoselectivity. The one-pot reaction involving a CuI/Pd0 cooperative dual catalyst directly addresses the need to develop more time-efficient and less-wasteful synthetic pathways.
Total synthesis of (+)-batzelladine A and (-)-batzelladine D via [4 + 2]-annulation of vinyl carbodiimides with N-alkyl imines
A diastereoselective [4 + 2]-annulation of vinyl carbodiimides with chiral N-alkyl imines has been developed to access the stereochemically rich polycyclic guanidine cores of the batzelladine alkaloids. Application of this strategy, together with additional key steps such as long-range directed hydrogenation and diastereoselective intramolecular iodo-amination, led to highly convergent total syntheses of (-)-batzelladine D and (+)-batzelladine A with excellent stereocontrol.
Arnold, Michael A.,Day, Kenneth A.,Duron, Sergio G.,Gin, David Y.
p. 13255 - 13260
(2008/03/11)
Stereogenic propargylic centers via base-mediated terminal allne isomerization
A study of alkali metal amide-mediated isomerizations of terminal allenes is described. The isomerizations of substituted ethenylidenecyclohexanes to form diastereomeric mixtures of terminal alkynes have been conducted to determine factors which may influence the stereochemistry at the newly formed propargylic centers. An initial base screen revealed that potassium N-methylbutylamide (KMBA) exhibits the highest level of equatorial to axial alkyne diastereoselectivity. With the severely hindered terminal allene 26, the use of potassium 3-aminopropylamide is required to effect isomerization. A general synthesis of deuterated terminal allenes has also been achieved, and a mechanistic study using d2-allenes 18a,b has revealed the involvement of a propargylic anion in the course of the KMBA-mediated isomerizations.
Spence, John D.,Wyatt, Justin K.,Bender, Daniel M.,Moss, David K.,Nantz, Michael H.
p. 4014 - 4021
(2007/10/03)
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