Enol ethers Simmons-Smith reaction

The Simmons-Smith reaction has been used as the basis of a method for the indirect a methylation of a ketone. The ketone (illustrated for cyclohexanone) is first converted to an enol ether, an enamine (16-12) or silyl enol ether (12-22) and cyclopropanation via the Simmons-Smith reaction is followed by hydrolysis to give a methylated ketone. A related procedure using diethylzinc and diiodomethane allows ketones to be chain extended by one carbon. In another variation, phenols can be ortho methylated in one laboratory step, by treatment with Et2Zn and... 

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. "... 

Cyclopentanones may also be synthesized from a,/ -unsaturated ketones and diiodo-methane. The ketone is converted to the O-silyl enol, and carbene is added to the enol double bond using the Simmons-Smith reaction (see p. 74f.). Thermal rearrangement of the resulting 1-siloxy-l-vinylcydopropane and add-catalyzed hydrolysis of the silyl enol ether leads to cyclopentanones in excellent yields (C. Girard, 1974). Very high temperatures, however, are needed, and this obviously limits the generality of this rearrangement reaction. 

J ,4i )-Pentane-2,4-diol was used as chiral auxiliary in the diastereo-differentiating Simmons-Smith reaction of the corresponding chiral enol ethers 53 to give a diastereomeric mixture of 54 and 55 in a ratio of ca. 96 4, which was found to be solvent dependent for the diethylzinc reagent. The major isomer was separated by recrystallization from a suitable solvent. 

The zinc(II) iodide promoted isomerization of siloxycyclopropanes to allyl silyl ethers was discovered during the study of the Simmons-Smith reaction of cyclic silyl enol ethers, where zinc(II) iodide is formed as a byproduct. ... 

Prepared in situ in the Simmons-Smith reaction of enol ethers. 

Conia and his co-workers ) modified the Simmons-Smith reaction ) by using enol ether plus predominantly diiodomethane/zinc-silver couple instead of the common known diiodomethane/zinc-copper couple ). This method is an excellent access to cyclopropanols and related compounds ) (Scheme 29). Furthermore,... 

An interesting study reports carbene additions to the androstane enol ether (139). Addition of dibromo- and dichloro-carbene gave the D-homo-a-halo-genoenones (140a) and (140b), respectively. The Simmons-Smith reaction on (139) afforded the l6a,17a-cyclopropyl steroid (141). Whereas treatment of (141) with acid provided the D-homo-derivative (142), reaction with iodine, followed by... 

Ring expansion of cycloalkanones. 1-Trimethylsilyloxybicyclo[n.l.0]alkanes (1), prepared by Simmons-Smith reaction with silyl enol ethers of cycloalkanones, react with ferric chloride in DMF containing pyridine to form a 3-chlorocycIo-alkanone (2) in fair to high yield. Dehydrochlorination (sodium acetate) yields a 2-cycloalkenone (3) containing one more carbon atom than the starting cycloalkanone. 

The enormous potential provided by the Simmons-Smith reaction is further demonstrated in an efficient one-pot synthesis of spiro-compounds of the type (10) by reaction of cyclic enol-silyl ethers with diethylzinc-methylene iodide this remarkable synthesis ca. 70% overall) proceeds via the three sequential reactions (7) (8), (8) (9), and (9)— (10). The versatile dichlorocarbene species is most conveniently generated under phase-transfer conditions using either KOBu -crown or NaOH-PhCHzNEts Cl. 

The synthetic potential of the Simmons-Smith reaction of trimethylsilyl enol ethers is still being explored. An interesting concentration effect has been noted in the reactions of the cyclic compounds (74 n = 3 or 4), which give the expected cyclopropanol derivatives (75) in dilute solution, but the 2-methylenecycloalkanols (76) in more concentrated solution. It was shown that (76) is formed via (75) by a zinc iodide-catalysed rearrangement. ... 

Advantage over Simmons-Smith is the homogeneity of the reaction and the high yields with enol ethers. (Not true for Sawada Reagent.)... 

Cyclopropanation of enol ethers, for example the conversion of 399 - 400, proceeds especially easy under Simmons-Smith conditions. This reaction offers additional options for the synthetic utilization of carbonyl compounds capable of forming enol ethers. Some of them will be considered later in this chapter (see Section 2.23.2). 

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