Trimethylsilyl-3-buten-2-one A Michael Acceptor

Submitted by Robert K. Boeckman, Jr.,1 David M. Blum,1 Bruce Ganem,2 and NEn. Hai.vey2 Checked by William R. Baker and Robert M. Coates 

Vinyltrimethylsilane (1). A 2-1., three-necked, round-bottomed flask is fitted with a mechanical stirrer, a reflux condenser, and a 500-ml. pressure-equalizing dropping funnel (Note 1). The flask is charged with 26.4 g. (1.1 mole) of magnesium turnings and 800 ml. of dry tetrahydrofuran (Note 2). A solution of 107 g. (72 ml., 1.0 mole) of vinyl bromide (Note 3) in 200 ml. of tetrahydrofuran is placed in the addition funnel and slowly added 

The condenser and dropping funnel are removed, and the flask is equipped for distillation with a 30.5-cm. Vigreux column. The distillate (b.p. 60-65°) is collected, transferred to a separatory funnel, and washed with 10-20 100-ml. portions of water (Note 7). The remaining colorless liquid, which amounts to 67-78 g. (67-78%), is predominantly silane 1, but contains small amounts of tetrahydrofuran (Note 8). 

3-Trimethylsilyl-3-buten-2-one (4). A solution of 55 g. of crude butenol 3 in 100 ml. of acetone is placed in a 500-ml., three-necked, round-bottomed flask equipped with a mechanical stirrer and a 250-ml. dropping funnel. The reaction vessel is immersed in an ice-water bath, and 95 ml. of an aqueous solution containing chromic acid and sulfuric acid (Note 13) is added to the stirred acetone solution. After completion of the addition, isopropyl alcohol is added to the reaction mixture until a green endpoint is reached, indicating consumption of the excess oxidant. The contents are poured into 450 ml. of ethyl ether, 300 ml. of water are added, and the aqueous layer is saturated with sodium chloride. The layers are separated, and the aqueous solution is extracted with five 150-ml. portions of ethyl ether. The combined ether solutions are washed with two 150-ml. portions of saturated aqueous sodium 

The apparatus is flamed dry under an argon atmosphere and maintained under argon during the reaction. 

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Annulation. 3-Trimethylsilyl-3-buten-2-one has been employed as a methyl vinyl ketone homolog in an improved method for the annulation of ketones. Based on work by Stork and Ganem, who employed 3-triethylsilyl-3-buten-2-one as a Michael acceptor in the Robinson annulation reaction, Suzuki and co-workers prepared a functionalized bicyclic ketone via a silyl enol ether as shown in eq 1. In general, the annulation of 2-alkylcycloketones with methyl vinyl ketone and its homologs produces rather poor yields of the desired cyclized products. 

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