Stereodivergent Direct Catalytic Asymmetric Mannich‐Type Reactions of α‐Isothiocyanato Ester with Ketimines

Abstract

Variabel: Sterisch gehinderte Produkte mit benachbarten tetrasubstituierten Kohlenstoffstereozentren, die nicht durch asymmetrische Hydrierung aufgebaut werden können, sind durch eine katalytische asymmetrische C‐C‐Verknüpfung zugänglich (siehe Schema; Dpp=Diphenylphosphinoyl). Der Wechsel des Gruppe‐2‐Metallzentrums ebnet einen stereodivergenten Weg zu α,β‐tetrasubstituierten α,β‐Diaminoestern.

Organocatalytic Morita–Baylis–Hillman/Michael/Acetalization Cascade: Procedure‐Controlled Diastereodivergence in the Asymmetric Synthesis of Fully Substituted Tetrahydropyrans

“…[1] This has inspired many efforts to achieve "diastereodivergence", in which a synthetic approach can be tweaked to selectively generate more than one of the possible diastereoisomer products from the same starting materials. [2] In monocatalytic systems, creating a diastereochemical switch generally means using different chiral catalysts, [3] different chiral ligands, [4] different Lewis acids [5] or substrates with different modifications. [6] In addition, the groups of Melchiorre [7a] and Yang [7b] independently documented that the judicious choice of acidic additives in symmetric aminocatalysis could switch the diastereochemical outcome when using a single chiral catalyst.…”

Highly Diastereo‐ and Enantioselective Mannich Reactions of Synthetically Flexible Ketimines with Secondary Amine Organocatalysts

“…Although the desired Mannich product 4 was formed in moderate to good yield in all of the solvents that were tested ( Table 1, entries [1][2][3][4][5], only a trace amount of 4 was isolated after chromatography on a silica gel column as a result of the low stability of 4. Therefore, 4 was treated with NaBH 4 in situ and converted into the corresponding g-lactone 5.…”

“…[1] Among these reactions, catalytic asymmetric Mannich reactions of ketimines that afford tetrasubstituted chiral carbon centers are rare, [2,3] and, with few exceptions, only aromatic ketimines are used as acceptors.…”

Direct Catalytic Asymmetric Vinylogous Mannich‐Type Reaction of γ‐Butenolides with Ketimines

“…[9][10][11][12] To date, the catalytic asymmetric vinylogous Mannich-type reaction of ketimines has only been addressed in an indirect manner utilizing 2siloxyfuran as the preformed vinylogous enolate and electrophilically activated a-acyloxy ketimines. [15] These circumstances and the synthetic utility of g-butenolides led us to develop the direct catalytic asymmetric vinylogous Mannich-type reaction of g-butenolide 1 with non-activated ketimines under proton-transfer conditions. [15] These circumstances and the synthetic utility of g-butenolides led us to develop the direct catalytic asymmetric vinylogous Mannich-type reaction of g-butenolide 1 with non-activated ketimines under proton-transfer conditions.…”