Silver-catalyzed cyclopropanation

For the rhodium-catalyzed cyclopropanation of olefin substrates with activated allylic C—H groups, the selectivity between cyclopropanation and C—H insertion is sometimes unsatisfactory. Very recently, Davies and Thompson (128) reported a selective silver-catalyzed cyclopropanation of olefins to give predominately cyclopropane products. Aryldiazoacetates were used as carbene precursors with the aryl groups helping to stabilize the carbene intermediate and facilitate the reaction. Notably, phenallyldiazoacetate with different olefins also gave cyclopropane products (Fig. 26). 

This silver-catalyzed ring rearrangement could be explained by preferential interaction of the silver cation with the most substituted edge of the cyclopropane to form an argento cation. In the latter, the presence of C-Si or Ge bond with the right orientation stabilized the cation sufficiently so that it classically evolved through (3-H... 

Figure 26. Silver-catalyzed selective cyclopropanation over allylic C—H activation.

A silver-catalyzed reaction of methyl ortfoi-fiarmylphenylpropargylate with alkenes led to a tandem 1,3-dipolar cycloaddition/cyclopropanation producing a series of polycyclic compounds with tetrahydrofuran moieties (140L4412). 

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. "... 

The total synthesis of ( + )-Erysotramidine (2) has been described by Ito et al. (137) starting from the amide (174) (Scheme 39). After O-mesylation to 177, base-catalyzed reaction gave the cyclopropane derivative (178) which with zinc in acetic acid was reduced to 179, which was identical to the product (135) of O-methylation of 172. Conversion of 178 to the thioketal (180) was followed by reaction with phenylselenyl chloride. A mixture of two compounds, 181 and 182, was produced the former could be transformed quantitatively to the latter. Finally, treatment of 182 with silver nitrate in methanol gave 183, which was then desulfurized to yield erysotramidine (2). 

The organothallium product is unstable to the reaction conditions, and decomposes to a mixture of acetate and olefin. A Hammett g value was determined for the reaction (—4.3). Lead salts also react with cyclopropanes 58,59). Recently extensive studies of the isomerization of strained cyclopropanes catalyzed by silver ions or by various transition... 

Upon Simmons-Smith cyclopropanation (CH2I2, Zn/Ag " or Zn/Cu ) vinylidenecyclo-propane gave a mixture of bicyclopropylidene (7) and dispiro[2.1,2.0]heptane (8). - An analogous reaction took place when 7-methylenedispiroheptane (9) was reacted with diiodo-methane and zinc-silver couple to give the trispiro[2.0.2.0.2.0]nonane (10) in quantitative yield.Small quantities of dispiro[2.1.2.0]heptane were isolated from the palladium acetate catalyzed reaction of vinylidenecyclopropane and diazomethane together with a variety of methylene insertion products. 

Silver(I) ions generally catalyze the rearrangement of strained polycyclic systems which contain cyclopropane groups. It was shown, however, that silver(I) cleaved one or two of the strained cyclopropane bonds in quadricyclane (13) in an oxidation reaction. A complex mixture was obtained on treatment of quadricyclane (13) with silver(I) trifluoroacetate. The main addition products contained two oxygen functions and one intact cyclopropane ring." °... 

Ladd CL, Sustac Roman D, Charette AB (2013) Silver-promoted, palladium-catalyzed direct arylation of cyclopropanes facile access to spiro 3,3 -cyclopropyl oxindoles. Org Lett 15 (6) 1350-1353... 

Similarly, oxime-derived isoquinoliniums can also be used for dipolar cycloaddition [90], The Wu group reported the interesting [3-1-3] cycloaddition of 180, generated from 179 by silver(I)-catalyzed cyclization, with activated cyclopropanes to produce 1,2-oxazine-fused isoquinoline derivatives 181 [91] (Scheme 19.46). 

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