Cyclopropyl trimethylsilyl ethers

This reaction has been carried out on cyclopropanols these substances, however, are less available (2, 118-119) than trimethylsilyl cyclopropyl ethers and are readily decomposed by the hydrogen bromide formed on bromination. In the new synthesis, the by-product is trimethylbromosilane. 

P-Bromo ketones. 3-Bromo ketones (3) can be obtained in high yield by bromination of trimethylsilyl cyclopropyl ethers (2), prepared with the Simmons-Smith reagent from trimethylsilyl cnol ethers (1). ... 

The cyclopropanation of 1-trimethylsilyloxycyclohexene in the present procedure is accomplished by reaction with diiodomethane and diethylzinc in ethyl ether." This modification of the usual Simmons-Smith reaction in which diiodomethane and activated zinc are used has the advantage of being homogeneous and is often more effective for the cyclopropanation of olefins such as enol ethers which polymerize readily. However, in the case of trimethylsilyl enol ethers, the heterogeneous procedures with either zinc-copper couple or zinc-silver couple are also successful. Attempts by the checkers to carry out Part B in benzene or toluene at reflux instead of ethyl ether afforded the trimethylsilyl ether of 2-methylenecyclohexanol, evidently owing to zinc iodide-catalyzed isomerization of the initially formed cyclopropyl ether. The preparation of l-trimethylsilyloxybicyclo[4.1.0]heptane by cyclopropanation with diethylzinc and chloroiodomethane in the presence of oxygen has been reported. "... 

F. Trimethylsilyl enol ethers are treated with Simmons-Smith reagent to form cyclopropyl silyl ethers. These rings undergo oxidative cleavage and ring expansion when treated with... 

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. 

A solution of 3-[l-(trimethylsilyl)cyclopropyl]cyclohex-2-enone (0.19 g, 0.91 mmol) in anhyd THF (10 mL) was added dropwise to a magnetically stirred slurry of benzyltrimethylammonium fluoride (0.18 g, 1.07 mmol) and benzaldehyde (0.24 g, 2.3 mmol) in THF (5 mL) at 0°C over 2 h. The reaction mixture was stirred for an additional 30 min and HjO (2mL) was added. The reaction mixture was transferred to a separatory funnel, diluted with EtjO (100 mL), and washed with brine (50 mL) and sat. NaHCOj (50 mL) prior to drying. Solvent evaporation gave a clear yellow oil which was chromatographed on silica gel (20% EtOAc/petroleum ether) yield 0.16 g (73%) as a clear oil which solidified to a white solid on standing at rt overnight mp 92 94.5 C. 

Cyclopentanone annelation via thermolysis of trimethylsilyl enol ethers of cyclopropyl methyl ketones has been studied a good yield of bicyclo[5,3,0]decan-8-one was obtained from (321 R = Q=CH2)OSiMe3 R = H), but only a low yield of bicyclo[5,3,0]decan-9-one was obtained from [321 R = H, R = C(=CH2)-... 

The Simmons-Smith reaction often starts very slowly and proceeds quite slowly at room temperature. The method of the preparation of active zinc-copper couple has been improved 93, 196, 298, 376, 443, 466). The use of zinc dust/cuprous chloride instead of zinc-copper couple gives higher yields in the Simmons-Smith reaction 407). The reaction with homoallylic alcohols of low reactivity was facilitated by use of excess Simmons-Smith reagent and distillation of ether to a halfvolume followed by heating in a stainless steel tube 182). The Simmons-Smith reaction was successfully applied to vinyl trimethylsilyl ethers to prepare, after methanolysis, cyclopropyl alcohols unobtainable by other methods 109). Here, the zinc-silver couple was used instead of the zinc-copper couple, and the quenching of the reaction mixture of the Simmons-Smith reaction was improved by using pyridine under nonaqueous conditions. 

Treatment of em-dibromocyclopropanes with one equivalent of alkyllithium at low temperature generates 1-bromocyclopropyllithiums, which have proved to be very versatile intermediates for the synthesis of various cyclopropyl derivatives. Thus, the reactions of the bromolithium compounds with disulfides ketones, alkyl ha-lides , methyleneammonium salts and trimethylsilyl chloride provide the corresponding 1-bromocyclopropyl derivatives (equation 124). A neighbouring ether... 

Formation of a C-H and a C-C bond at the expense of a C-Br and a C-Si bond occurs when 1 -bromo -1 -trimethylsilylcyclopropanes are treated successively with butyllithium and dichloro-methyl methyl ether at — 95°C and yield cyclopropyl trimethylsilyl ketones The 1-... 

Thus, trimethylsilyl ethers, such as 1, generated from cyclopropyl ketones, were reacted with a selenyl chloride as electrophile. 

The oxidation of cyclopropyl trimethylsilyl ethers by copper(II) tetrafluoroborate probably proceeds via cation radicals which ring open and, in suitably substituted examples, cyclize. The main cyclopentyl ketone products were formed as mixtures of stereoisomers and were accompanied by many side products. ... 

Cyclopropyl trimethylsilyl ethers, which were readily prepared from aldehydes, ketones and esters, coupled with alkenes on treatment with mercury(II) acetate and, after reduetion with sodium borohydride, afforded chain-extended carbonyl compounds, e.g. 37, in moderate to good yields. The whole reaction could be carried out in one pot. 

Oxidative cleavage of cyclopropyl trimethylsilyl ethers. 2-Cycloalkenones are... 

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