[64556-66-7] · C5H11BrOSi · (Z)-2-Bromo-1-(trimethylsilyloxy)ethylene · (MW 195.13)
(reagent used as a precursor of (Z)-(trimethylsilyloxy)vinyllithium, a-bromo aldehydes, and a-disilylketene)
Physical Data: bp 48-49 °C/15 mmHg.1
Solubility: sol Et2O, THF and most organic solvents; fairly sol cold water.
Analysis of Reagent Purity: 1H NMR (C6D6) (Z) isomer: 6.37 (d; J = 3.8); 5.02 (d; J = 3.8); 0.05 (s). (E) isomer: 6.61 (d; J = 11.4); 5.52 (d; J = 11.4); -0.06 (s).
Preparative Methods: addition of Bromine to trimethylsilyl vinyl ether in CH2Cl2 or Et2O at -60 °C, followed by dehydrobromination with Triethylamine (50%)1 or by reaction of trimethylsilyl 2,2-dibromoethyl ether with two equiv of n-Butyllithium in Et2O from -70 °C to rt (86%)2 (Z/E:95/5).3
Purification: vacuum distillation.
Handling, Storage, and Precautions: must be stored at -20 °C in the absence of moisture (flushing with dry Ar or N2). It turns pale yellow on storage. It is instantaneously hydrolyzed by dilute acidic aqueous solutions.
(Z)-2-Bromo-1-(trimethylsilyloxy)ethylene (1) is used essentially as a precursor of (Z)-2-(Trimethylsilyloxy)vinyllithium (eq 1).3
Reagent (1) has been condensed with allylic alcohols in the presence of a catalytic quantity of a Lewis acid (such as Boron Trifluoride Etherate) to achieve a new synthesis of a,b-unsaturated aldehydes (eq 2).4 This reaction is analogous to the widely used Müller-Cunradi-Pieroh reaction5 except that the oxidation state of the cationic species is one unit lower and that of the nucleophilic species is one unit higher. Thus condensation with b-ionol leads to an a-bromo aldehyde which was transformed into b-ionylideneacetaldehyde by dehydrobromination, using 1,8-Diazabicyclo[5.4.0]undec-7-ene.4
The reaction of (1) with Lithium Diisopropylamide followed by treatment with Chlorodimethylsilane was reported to give the disilylketene (2) in a modest yield,6 instead of the expected alkynic ether (3) (eq 3).2 The hydridosilylketene (2) is transformed by flash vacuum thermolysis (FVT) to trimethylsilylacetylene by expulsion of dimethylsilanone.6
It is noteworthy that compounds homologous with (1) couple with Grignard reagents in the presence of nickel-phosphine complexes to produce alkylated and arylated enol ethers (eq 4).7
University of Rouen, France