[23184-28-3] · C7H17NOSi · N,N-Dimethyl-2-(trimethylsilyl)acetamide · (MW 159.34)
Physical Data: bp 67-69 °C/4 mmHg; 47-49 °C/0.2 mmHg.
Preparative Methods: although the direct trimethylsilylation of the lithium enolate of N,N-dimethylacetamide3a is the most straightforward approach to the title reagent, other a-silyl amides have been prepared by amidation of the corresponding esters.4 The reaction of aminosilanes with ketene gives the O-trimethylsilylated isomer, which thermally rearranges to the a-trimethylsilylamide.5 In reactions of chlorosilanes with the lithium enolates of amides, larger silyl groups such as the t-butyldimethylsilyl group tend towards O-silylation, and smaller groups on nitrogen lead to C-silylation.3a Thermal isomerization leads to the C-silylated tautomer as the major product (eq 1). The direct C-dimethylphenylsilylation of the lithium enolate of N-methyl-d-valerolactam has been reported (eq 2).6
Reaction of N,N-dimethyl-2-(trimethylsilyl)acetamide with either Lithium Diisopropylamide or n-Butyllithium in THF at 0 °C provides the lithium enolate, which is stable at rt for several days. This enolate reacts with aldehydes and ketones to produce a,b-unsaturated amides via the condensation-Peterson elimination sequence (eq 3). This reaction was employed in an approach to (±) cherylline (eq 4).7
The reaction of the lithium enolate of N,N-dimethyl-2-(trimethylsilyl)acetamide with aromatic nitrones gives a-aryl-a,b-unsaturated amides in modest yields (eq 5).8 The reaction of the lithium enolate with amides yields b-amino-a,b-unsaturated amides (eq 6),2 and the reaction with propene oxide leads to N,N-dimethyl-4-(trimethylsiloxy)pentanamide (eq 7).1
The direct a-trimethylsilylation of b-lactams and the intermediates used in the synthesis of this important class of compounds have been reported.9
Gerald L. Larson
Hüls America, Piscataway, NJ, USA