Silver Simmons-Smith cyclopropanation

Vinylcyclopropanols can be prepared either from the readily available cyclopro-panone hemiacetaP, from 1-hydroxycyclopropanecarboxaldehyde derivativesfrom a,a -dichloroacetone, from the silver Simmons-Smith cyclopropanation of a-ethylenic ketone silyl enol ethers from the dye-sensitized photo-oxygenation of alkylidene-cyclopropanes or from the ring-opening of oxaspiropentanes (cf. Section III.C). Consequently, they become participants of choice in a number of useful chemical transformations (see also Section IV.A). 

Sigmatropic rearrangement 677, 697 Sihca gel membranes 1082 Silphinene, electrosynthesis of 1183, 1187 Silver compounds, as oxidants 1307-1311 Silybin, synthesis of 1308, 1310 Silydianin 1180 Silylation, of phenols 934, 935 Silylcyanation, asymmetric 694, 695, 702 Simmons-Smith cyclopropanation, asymmetric 694... 

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. 

The intramolecular cycloaddition of the Simmons-Smith cyclopropanation product 30 of nor-born-5-en-2-one trimethylsilyl enol ether 29 is promoted by donor substitution and/or silver catalysis. ... 

A review on the Simmons-Smith cyclopropanation has appeared. The involvement of silver carbenoids in various reactions (including Wolff rearrangement, car-benoid additions, and insertions) has been discussed. Benzannulation carried out by addition of a Fischer carbene to an alkyne (Doetz reaction) has been presented in an historical perspective featuring mechanistic details and synthetic applications. ... 

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 selective cyclopropanation of the a-enone silyl enol ether 75, by methylene iodide and the zinc-silver couple 2), is remarkable. Only the double bond bearing the tri-methylsiloxy group reacted to yield the 1-trimethylsiloxy vinylcyclopropane 76 when not more than 1.1 equivalent of the Simmons-Smith reagent was used, but the bis-cyclopropanation product 77 was obtained in good yield with an excess (3 equivalents) of the cyclopropanating reagent, Eq. (24) 42). 

Improved reaction. Conia et al. have reported two modifications of the Simmons-Smith reaction which ave improved yields. One is the use of a zinc-silver couple in place of the zinc copper couple. This couple is prepared by adding granular zinc to a stirred hot solution of silver acetate in acetic acid. The mixture is stirred for 30 sec. and the zinc-silver couple formed is isolated by decantation and washed with acetic acid and ether. It is then stabilized by addition of a small amount of silver wool. The second improvement is that the reaction mixture is not subjected to acid hydrolysis. Instead an amine, for example pyridine, is added. This forms the insoluble complexes Znlj-C HsN and ICH jZnl -(C, 115N)j the cyclopropane products are then isolated from the filtrate. 

This sequence has been used for the synthesis of the sesquiterpenes ( —)- and ( + )-thujop-sene. The allylic /1-hydroxysulfoximines 47 and 49 were separated by column chromatography on silica gel and treated separately with excess of Simmons Smith reagent prepared from zinc/ silver amalgam and diiodomethane in diethyl ether giving 48 and 50, respectively. The Simmons-Smith reaction took place stereospecifically cis to the hydroxy group of the allylic ff-hydroxysulfoximines. Cyclopropanes 48 and 50 were converted to ( —)- and (- -)-thujopsene. 

SUica gels, 110, 221, 229, 339, 345, 416, 461,505,509 a-Siloxyallylsilanes, 485 Silver acetate, 441-442 Silver carbonate, 441 Silver carbonate-Celite, 441-442 Silver chromate-iodine, 442 Silver cyanide, 442 Silver fluoride, 161 Silver nitrate, 247 Silver(I) oxide, 441, 442-443 Silver tetrafluoroborate, 443-444 Silverll) trifluoroacetate, 444-445 Silver(II) trifluoroacetate, 527 Silylation, 227 Silyl cyclopropanes, 307 Silyl enol ethers, 127, 172, 218, 227, 296, 378, 446, 485, 524-525 Silylvinyl triflates, 410 Simmons-Smith reagent, 172,445 Smiles rearrangement, 243 Sodium, 445... 

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