Dichloromethyl ethers, reaction with lithium

Chiral boronic esters react with organolithium reagents to form diorganylalkoxyboranes (borinic esters). Subsequent reaction with the anion of dichloromethyl methyl ether then yields chiral ketones by rearrangement of both of the groups on boron (Scheme 42). No racemization is observed in this sequence and alkyl-, aryl- or alkynyl-lithium reagents can be used. 

Nakajima has shown that a-cyclopropyl acyl silane (23) results from reaction of 1-trimethylsilyl cyclopropyl lithium with dichloromethyl methyl ether at low temperature in THF solution, in a reaction said to involve a carbene intermediate and a 1,2-silicon shift (Scheme 56)147. 

Summary Methoxy-bis[tris(trimethylsilyl)silyl]methane (4), the first geminal di(hyper-silyl) compound with a central carbon atom, was prepared by the reaction of tris(tri-methylsilyl)silyl lithium with dichloromethyl methyl ether. The structure of 4, which is characterized by considerable distortions due to the spatial demand of the two (MesS aSi groups, is discussed on the basis of an X-ray crystal structure analysis. 

A 100-mL round-bottom flask containing a magnetic stirrer is capped with a rubber septum and charged with 15 mmol of borinate. 15 mL of diethyl ether arc added and the reaction is cooled to 0°C. 2.04 mL (22.5 mmol) of dichloromethyl methyl ether are added followed by 16.2 mL (30 mmol) of lithium lert-bu-toxide. The ice bath is removed and the mixture stirred at r.t. for 1 h. A slightly exothermic reaction develops and a white precipitate forms. The reaction mixture is cooled to 03C and 18 mL (45 mmol) of pH 8 phosphate buffer arc added, followed by 5.1 mL (45 mmol) of 30% hydrogen peroxide. The ice bath is removed and the mixture stirred for 12 h. The phases are separated, the aqueous phase extracted with two 15-mL portions of diethyl ether, the combined extracts washed with two 15-mL portions of water, then aq NaCl, dried over MgS04 and filtered. The volatiles are removed under reduced pressure and the residual oil is purified by bulb-to-bulb distillation. The chemical purity of the ketones is determined by GC using a 5% SP 2100 on Chromosorb W column and is usually >95%. The chiral ketones are further purified by preparative GC. For further examples, see Table 2. 

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