Silicon‐Derived Singlet Nucleophilic Carbene Reagents in Organic Synthesis

Abstract

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Visible‐Light‐Induced Cycloaddition of α‐Ketoacylsilanes with Imines: Facile Access to β‐Lactams

“…As for the generation of ketenes by photolysis, two possibilities of the photorearrangement were considered. One process involves a single-step [1,3]-silyl shift [20] to the distal carbonyl group. Alternatively, a two-step mechanism, that a [1,2]-shift of silicon to the adjacent carbonyl group with generation of a siloxycarbene, followed by a Wolff rearrangement, could be operative.…”

“…The n!p* triplet state 3 A was shown to be the lowest excited triplet state, whose population from 1* A was computed to be thermodynamically favorable (DG 1*A/3A = À9.7 kcal mol À1 ). From triplet state 3…”

“…With our continuing interest in acyl silane chemistry, [5h] we turned our attention to a-ketoacylsilanes, which are a rarely explored class of compounds. [14] Besides [1,2]-silyl migration of acylsilanes to form siloxycarbenes, we envisaged that a-ketoacylsilanes could theoretically undergo [1,3]-silyl migration to form ketene intermediates. Herein, we report a mild, visible-light-induced method to generate ketenes from a-ketoacylsilanes without additives such as stochiometric base or metal, and their cycloadditions with imines (Scheme 1 b).…”

Durch sichtbares Licht vermittelte Cycloadditionen von α‐Ketoacylsilanen mit Iminen: Einfache Synthese von β‐Lactamen

“…Als Pionierarbeit von Brook und Mitarbeitern kçnnen Siloxycarbene photochemisch über die 1,2-Brook-Umlagerung aus Acylsilanen erzeugt werden (Schema 1 a). [3] Im Allgemeinen entsprechen die Reaktivitätsmuster von Siloxycarbenen der nukleophilen Carbenchemie, [3,4] die auf die Resonanzstabilisierung des Singulett-Zustands durch Donor-Substituenten zurückgeführt werden. Solche Zwischenprodukte besitzen die Fähigkeit, (i) eine X-H-Insertion einzugehen (X = C, N, O, Si, B, etc.…”

“…Für die Erzeugung von Ketenen durch die photochemischen Bedingungen wurden zwei Mçglichkeiten der Umlagerung betrachtet. Ein Prozess beinhaltet eine einstufige [1,3]-Silylverschiebung [20] zur distalen Carbonylgruppe. Alternativ kçnnte ein zweistufiger Mechanismus,d.…”