Simmons-Smith procedure

Carbene itself is extremely reactive and gives many side reactions, especially insertion reactions (12-19), which greatly reduce yields. When it is desired to add CH2 for preparative purposes, free carbene is not used, but the Simmons-Smith procedure (p. 1088) or some other method that does not involve free carbenes is employed instead. Halocarbenes are less active than carbenes, and this reaction proceeds quite well, since insertion reactions do not interfere.The absolute rate constant for addition of selected alkoxychlorocarbene to butenes has been measured to range from 330 to 1 x 10 A few of the many ways in... 

Several modifications of the Simmons-Smith procedure have been developed in which an electrophile or Lewis acid is included. Inclusion of acetyl chloride accelerates the reaction and permits the use of dibromomethane.174 Titanium tetrachloride has similar effects in the reactions of unfunctionalized alkenes.175 Reactivity can be enhanced by inclusion of a small amount of trimethylsilyl chloride.176 The Simmons-Smith reaction has also been found to be sensitive to the purity of the zinc used. Electrolytically prepared zinc is much more reactive than zinc prepared by metallurgic smelting, and this has been traced to small amounts of lead in the latter material. 

Gem-dibromospiropentane (620), obtained by the reaction of MCP with dibromocarbene, was used in the synthesis of BCP (3) (Scheme 90) [6a]. The reaction of the intermediate vinylidenecyclopropane 621 with a large excess of Simmons-Smith reagent gave exclusively BCP (3), but using modified Simmons-Smith procedures the [3]-triangulane (247) was also obtained in small yield (Scheme 91) [165],... 

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 ... 

The reaction of carbenes with appropriately substituted olefins provides a useful method for the preparation of many cyclopropanone derivatives. The Simmons-Smith procedure 22> and reactions involving base-generated carbenes, e.g. CHC13/KO-7-Bu, are particularly useful. 

The addition of a-lithiovinyltrimethylsilane 151 83), generated from a-bromovinyl-trimethylsilane84,) with r-BuLi (1.5 equivalents) at —78 °C in ether, to ketones and aldehydes was also investigated. The allylic alcohols 152 thus obtained underwent smooth cyclopropanation when the modified Simmons-Smith procedure utilizing EtZnI85) was applied. The cyclopropylcarbinols 153 were directly dehydrated without rearrangement upon exposure to catalytic amounts of p-TsOH in benzene at 20 °C to give 149 in yields of 52-75%, Eq. (48) 79,8L). 

Finally, a fairly convenient protocol for carbene transfer reactions utilizes species like ICH(R)ZnI (a carbenoid), generated in situ by the interaction of 1,1 -di-iodides, RCHI2, with a zinc-copper pair (Simmons-Smith procedure, reaction... 

Asymmetric induction is possible when chiral additives are used. With the Simmons-Smith procedure, as with free carbenes, conjugated dienes give 1,2-addition, and allenes give methylenecyclopropanes or spiropentanes. ... 

Alkenylboronic acids 58 were esterified with chiral diols [e.g. ( + )-diisopropyl tartrate] and the ester 59 subjected to the original Simmons-Smith procedure to give the cyclopropyl derivatives 60 as the intermediate product. Cyclopropyl derivative 60 was directly oxidized with alkaline 30% hydrogen peroxide to /ranj-cyclopropanols 61 in 73-86% ee. This method gives access to secondary cyclopropanols bearing a vicinal substituent. 

Diphenylcyclopropane has been prepared previously by (1) the Simmons-Smith procedure (24% yleld) b,19 and modified versions of this method (up to 72%),20 (2) sulfonium ylide addition to 1,1-diphenylethene (61% yield),21 (3) reduction of 1,1-diphenyl-2,2-dihalocyclopropanes with sodium in ammonia (47% yield),22 with sodium and tert-butyl alcohol (80%), or with diethyl lithiomethanephosphonate (62%),23 (4) base-promoted cyclization of trimethyl(3,3-diphenylpropyl)ammonium iodide (78%),24 (5) boron trifluorlde-promoted cyclization of a corresponding 3-hydroxypropyistannane (97%),2 (6) reaction of 3,3-diphenylpropenoic acid with lithium aluminum hydride (62%),2 (7) reaction of... 

X = CN in 8-3) by Ciganek (1967). A more generally applicable route to norcara-diene derivatives was realized by the Simmons-Smith procedure (1959) using CH2I2 and a Zn — Cu couple (which may be called a carbenoid reagent, yet in a somewhat broader sense than the term carbenoid is used today, see Sect. 8.7). 

The Pd(OAc)2-mediated reaction can be used to cyclopropanate electron-deficient alkenes as well as terminal alkenes. Thus selective reaction at a monosuhstituted aUcene in the presence of others is readily achieved using this method (eq 43). The example shown in eq 44 is one in which the Simmons-Smith procedure failed to provide any of the desired product, whereas the current method provided a 92% yield of cyclopropane. ... 

Carbocyclic Ring Formation-A mixture of Zn dust and a cuprous halide apparently functions as efficiently as a Zn-Cu couple in the Simmons-Smith procedure, and is more convenient. The high yield, preparative scale electrochemical synthesis of phenylcyclopropane and cyclopropanol from the corresponding 1,3-dibromides has been reported. ... 

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