Nucleophilic Attack of Siloxycarbenes on Carbonyl Groups. The Formation of Oxiranes

Abstract

Siloxycarbenes, formed by the photolysis of dimethyl- or diphenylsilacyclohexanone have been trapped as oxiranes or as the ring-opened hydrolysis products of oxiranes, with simple aldehydes and ketones such as acetaldehyde, or cyclohexanone. The reactions are interpreted as arising from the nucleophilic attack of the siloxycarbene on the carbonyl group. The structures of the oxiranes and their hydrolysis products have been established.

Lewis Acid‐Assisted Photoinduced Intermolecular Coupling between Acylsilanes and Aldehydes: A Formal Cross Benzoin‐Type Condensation

“…This result prompted us to develop photoinduced cross benzoin‐type reaction for preparation of α‐hydroxyketones by utilizing siloxycarbenes as an acyl anion equivalent. Although a closely related work has been already reported by Brook and co‐workers, the reaction was limited only to 2‐silacyclohexanone 3 as an acylsilane unit (Scheme , equation b) . Thus, intermolecular coupling of readily available acyclic acylsilanes with aldehydes remains unexplored.…”

Photoisomerization of Acylsilanes to Siloxycarbenes, and Their Reactions with Polar Reagents

“…the effectiveness of trapping agents would depend either on their proton donating or electron donating ability. Evidence has already been published which demonstrated that cyclic siloxycarbenes from silacyclohexanones were strongly nucleophilic in nature, forming a cyclopropane adduct with the electron-deficient olefin, diethyl fumarate (9), or oxiranes via nucleophilic attack of the carbonyl group of aldehydes and ketones (10). The photochemistry of the acyclic acylsilanes (none of which were found to form related cyclopropanes or oxiranes in detectable amounts) is also most readily interpreted on the basis of the siloxycarbene being markedly nucleophilic.…”

Photochemical reactions. 146th communication. Photochemistry of conjugated methano‐epoxydienes: Participation of the neighboring cyclopropane ring in product formation via carbonyl ylide and carbene intermediates

“…4, 70.5 (24 C(2'), C(4')); 141.0 (s, C (3)). MS: 218 (1 1, M +, C,5H,20), 203 (22), 177 (16), 175(12), 162(36), 161 (26), 159(11), 147(40), 145(20), 135 (15), 134(15), 133(25), 131 (lo), 123(36), 121 (49, 120 (18), 119(90), 117 (13), 109 (12), 108 (15), 107(46), 106(26),105(100),95 (24),93(35),91 (55),81 (23),80(11),79 (38),77 (39,69 (IS),67 (39,65 (19), 57 (II), 55 (33), 53 (22), 51 (12) (23,000). IR: 3085m, 3005s, 2962s, 2934s, 2920s, 2875m, 2850m, 1780w (br.…”

“…"C-NMR: 18.6, 20.0, 28.1, 28.9 (4q, 4 CH,); 9.6 (1, C(8')); 34.3 (t, C(6')); 116.5 (t. C(4)); 11.5, 15.4 (24 C(l'), C(7')); 127. 5,135.9 (24 C(l), C(2)); 33.2 (s, C(5')); 67.4,70.2 (2s, C(2'), C(4')); 140.8 (12), 108 (13), 107 (42), 106 (25), 105(100), 95 (21), 93 (35), 92 (IS), 91 (60), 81 (20), 80 (II), 79 (41), 78 (lo), 77 (36), 69 (14). 67 (31), 65 (19).…”

“…Thus, it could be assumed that from (E)-7, the carbene f is formed in a conformation, prone to undergo fragmentation to 11. On the It was shown previously that the reaction of carbenes with carbonyl compounds led to oxiranes [13] or to carbonyl ylides [14-161. For reviews on the reactivity of a-cyclopropyl carbenes, see (171 [18]; for a theoretical interpretation, see [19].…”