Olefins Simmons-Smith reagent

A cis addition mechanism is generally accepted for the reaction, because cis addition to an olefinic bond generally occurs with predominant attack at trans bonds, and the Simmons-Smith reagent attacks preferentially one of the trans olefinic bonds of trans,trans,cis-1,5,9-cyclodode-catriene and then the cis double bond of the monoadduct (378). The close correspondence in relative rates of olefins for the cyclopropane formation by the Simmons-Smith reaction with those for diimide reduction and peroxide epoxidation supports the concept 409). The latter two reactions are generally considered to proceed via cis addition. 

Solutions of (I), (VIII), and (IX) in ether react with olefins to give the corresponding cyclopropane derivatives 200, 427a, 542-546). Burger and Huisgen 64) concluded that the Simmons-Smith reagent [CH2I2 +... 

The reaction of aldehydes with the Simmons-Smith reagent in the presence of an excess amount of zinc dust gives the corresponding olefins in 29-63% yields (192, 193, 341). The reaction is nucleophilic, unlike... 

Usually zinc carbenoids do not insert into olefinic C—H bonds, although the Simmons-Smith reagent was reported to attack ether to give products resulting from insertion of a methylene group into the a-C—H bond 42, 185). As has been mentioned above, the formation of methyl-acetylene derivatives from terminal acetylene derivatives may proceed via insertion of methylene into the C—H bond 528). 

Syntex workers7 later found that (3) can be dehydrogenated to (5) directly by DDQ in 90% yield (2.5 moles of DDQ, refluxing dioxane, 1-2 hrs.). This oxidation of an unactivated disubstituted olefin to a diene is rare a related reaction to the oxidation of tetramethylethylene to 2,3-dimethylbutadiene (2, 117). They then found that it was possible to shorten the original synthesis even further. Reaction of (1) with a modified Simmons-Smith reagent (this volume) gave (3) directly in 50% yield. The overall yield of (5) from naphthalene is thus about 40%. 

The synthesis of the steroidal 2a,3a-cyclopropanol (137b) has been described. The 3-bis-(2-chloroethoxy)-derivative (135) was pyrolysed in vacuo to give the olefin (136). This with excess Simmons-Smith reagent gave the cyclopropyl steroid (137a), which with butyl-lithium liberated the free cyclopropanol (137b) this was converted into 17j8-hydroxy-2a-methyl-5a-androstan-3-one (138) by base. 

General Methods.—The preparation of cyclopropanes by addition of the Simmons-Smith reagent [from CHjla + Zn (Cu)] to olefinic substrates has been a cornerstone in synthesis for almost two decades. Kawabata and co-workers have now described a seemingly more convenient procedure which uses copper in place of the familiar zinc-copper couple and produces cyclopropanes in comparable yields. In addition, the procedure can be employed with trihalogenomethanes and dibromo-acetates leading to monohalogenocyclopropanes and cyclopropane carboxylates, respectively, both with 5> n-stereoselectivity (Scheme 2). 

In 1958 Simmons and Smith described a new and general synthesis of cyclopropanes by treatment of olefins with a reagent prepared from methylene iodide and a zinc-copper couple in ether solution. 

The transition metal-catalyzed cyclopropanation of alkenes with diazomethane is a valuable alternative to Simmons-Smith methodology [645]. Because of the mild reaction conditions under which this reaction takes place, diazomethane is the reagent of choice if sensitive olefins are to be cyclopropanated [646-648]. 

Asymmetric cyclopropanation of olefins can also be achieved by the Simmons-Smith reaction (231). Reaction of ( )-cinnamyl alcohol and the diiodomethane-diethylzinc mixed reagent in the presence of a small amount of a chiral sulfonamide gives the cyclopropylcarbinol in up to 75% ee (Scheme 97) (232a). ( )-Cinnamyl alcohol can be cyclopro-... 

Diiodomethane with zinc-copper couple is a particularly good reagent for the insertion of a methylene group into an olefinic bond. The reaction is known as the Simmons-Smith procedure,10 and is likely to proceed as follows ... 

Cyclopropanes are commonly synthesized with Zn(CH2I)2 (37) using the Simmons-Smith-reactum.16 This reaction proceeds via one-step addition of one of the methylene groups of the zinc reagent to olefins. As an advantage of the Simmons-Smith-reaction no free carbene is involved. 

A number of modifications of the original Simmons-Smith cyclopropanation procedure have been reported. Furukawa s reagent, (iodomethyl)zinc derived from diethylzinc and diiodomethane, ° or its modification using chloroiodomethane instead of diiodomethane, ° allows more flexibility in the choice of solvent. The reagent is homogeneous and the cyclopropanation of olefins can be carried out in non-complexing solvents, such as dichloromethane or 1,2-dichloroethane, which greatly increase the reactivity of the zinc carbenoids. 

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