The influence of (organo)metallics “metal-tuning” on stereo- and regio-chemical convergence in reactions of allylic carbanions with aldehydes

Preparation of α-substituted γ-alkoxyallylstannanes from β-tributylstannyl acrolein acetals: scope of the method and primary rationalization of the obtained results

“…When the cyclic acetal 1cE was used as starting material (entries 13,14), once more the S N 2 0 substitution products 2j and 2k were obtained but as a mixture of E-and Zisomers. The weakness of the diastereoselectivity can be solved starting from 1cZ (2k and 2l were obtained as pure Z-isomers) but another contamination due to the S N 2 products 3k and 3l (respectively, 10% and 15%) was observed (entries 15,16).…”

“…Hydrostannation of alkoxyallenes under free radical conditions or under palladium catalysis usually affords a mixture of isomers [10][11][12] while metallation of allyl acetals [13] or allyl ethers [14,15] followed by quenching with a triorganotin halide works nicely with a strong preference for the Zisomer in the last case due to the chelation of the metal with oxygen.…”

Enantiospezifische Synthese und Allylierung ausschließlich Kohlenstoff‐substituierter, α‐chiraler Allylstannane

“…[19,20] Die kupferkatalysierte Kohlenstoff-ZinnBindungsknüpfung führte auch tatsächlich zum enantiomerenangereicherten difunktionellen Synthesebaustein (R)-14 (Schema 4), doch war dieser zu instabil für weitere Syntheseoperationen. Kontrollversuche bestätigten, dass schon BF 3 ·OEt 2 allein in der Lage ist, (R)-14 innerhalb von Minuten quantitativ zu zersetzen, während (R)-9 einigermaßen stabil gegenüber Lewis-Säuren ist.…”

“…In einem ersten Ansatz, die Anwendungsbreite der vorgestellten Reaktion zu erweitern, nutzten wir das siliciumhaltige Benzoat (S)-13 für einen enantioselektiven Einstieg in die attraktive Chemie zinn-und siliciumfunktionalisierter Allylbausteine. [19,20] . Stichwörter: Allylierungen · Allylische Substitutionen · Enantiospezifität · Stannane · Stereoselektive Synthesen…”

Catalytic Enantioselective Addition of Organozirconium Reagents to Aldehydes

“…Organozirconium reagents [ 42 , 43 , 44 , 45 , 46 , 47 , 48 ] are relatively inert toward carbonyl compounds [ 49 ], but the use of catalysts or a stoichiometric mediator [ 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ] enables the nucleophilic attack and subsequent carbon-carbon bond formation. Thus, in the presence of Ag(I), ZnBr 2 , or Me 2 Zn, organozirconium reagents can readily be added to aldehydes [ 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ], ketones [ 69 , 70 ], and also enones [ 71 , 72 , 73 , 74 ], epoxides [ 75 ], and isocyanates [ 76 ], although enantioselective protocols have been rare so far [ 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 ,…”