Diiodomethane-Diethylzinc

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-... 

Asymmetric induction in the cyclopropanations of unsaturated substrates with methylene has been extensively investigated. A propensity of the Simmons-Simth and related reagents to make coordination to basic atoms is most frequently exploited. Treatment of a,/J-unsaturated aldehyde acetals derived from the aldehydes and chiral dialkyl tartrates or 2,4-pentanediol, with diiodomethane/diethylzinc in hexane, produces cyclopro-panecarboxaldehyde acetals with high diastereoselectivity (equation 69)109 110. Uniformly good diastereoselectivity has also been realized in the cyclopropanations of chiral acetals... 

Camphor- 10-sulfonic acid, 62 (S)-2-(l-Hydroxy-1-methylethyl)-pyrrolidine, 146 a-Methylbenzylamine, 185 Quina alkaloids, 264 Cycloaddition reactions 2-Oxazolidones, chiral, 225 Cyclopropanation Diiodomethane-Diethylzinc, 276 Simmons-Smith reagent, 275 Deprotonation Lithium amides, chiral, 159... 

Trimethylamine N-oxide, 325 Vinyltrimethylsilane, 343 Other reactions (Phenylsulfonyl)allene, 247 Cyclodehydration Diethoxytriphenylphosphorane, 109 Hexamethylphosphoric triamide, 142 Cycloprop anation Simmons-Smith reaction Diiodomethane-Diethylzinc, 276 Simmons-Smith reagent, 275 by other reagents which add CH2 to a carbon-carbon multiple bond Dibromomethane-Zinc-Copper(I) chloride, 93... 

Dicarbonyl(cyclopentadienyl)-[(dimethylsulfonium)methyl]-iron(II) tetrafluoroborate, 98 Diiodomethane-Diethylzinc, 276 Diiodomethane-Triisobutylalu-minum, 114... 

Diiodomethane-Diethylzinc, 276 2-Oxazolidones, chiral, 267 8-Phenylmenthol, 243 (S)-Prolinol, 261 Simmons-Smith reagent, 275 L-Valinol, 341 Amides... 

Diethylzinc-Titanium(IV) chloride, 21 Diiodomethane-Diethylzinc, 276 Diiodomethane-Zinc-copper couple, 275... 

In contrast to the reaction with diazomethane, the cyclopropanation of cyclopropylidene(di-spiro[2.0.2.1]heptylidene)methane (15) with diiodomethane/diethylzinc took place predominantly at the reactive central double bond. The product of double cyclopropanation was also obtained in good yield. 

The carbenoid generated from diiodomethane/diethylzinc is often found to be more reactive than the conventional Simmons-Smith reagent. Thus, in the case of 1-alkenylboronic acid esters, where diazomethane failed to cyclopropanate trisubstituted derivatives (Section 1.2.1.1.1.) diiodomethane/diethylzinc gave good yields of the required products 16. ... 

Another modification with trialkylaluminum compounds as the metalating agent (see Table 1) is reported to occur stereospecifically but without any diastereoselectivity7 (for a procedure see Vol. E 19b. p 209). Interestingly, this carbenoid source exhibits a rather different chemoselectivity compared to the diiodomethane/diethylzinc combination the preference for allylic alcohols with the latter reagent to react with.yyn stereoselectivity (see Section 1.6.1.5.1.2.) is not observed with the aluminum-based reagent. 

The silyl enol ether prepared from (-)-menthone is transformed into a mixture of two diastereo-meric optically active cyclopropane derivatives by the diiodomethane/diethylzinc reagent28. 

Acetals from a,/3-unsaturated aldehydes and optically active 1-aryl-1,3-propanediols are cyclopropanated by the diiodomethane/diethylzinc reagent with moderate selectivity69. After oxidative cleavage of the auxiliary, cyclopropanecarboxylic acids are obtained with 21 -78% ee. Thus, the C2-symmetric auxiliaries seem to be superior for this kind of [2 + 1] cycloaddition. 

Treatment with triisobutylaluminum converts the saturated acetal 6 into the optically active enol ether 770. Cyclopropanation of 7 with the Simmons-Smith reagent then provides the cyclopropanol derivative 8 with a d.r. of 95 5. Even better side discrimination is observed when the more active diiodomethane/diethylzinc system is applied under optimized conditions70 the cyclopropanol derivative is obtained diastereomerically almost pure. 

Cyclopropanation of eA o-A-[(lf ,25,3/ ,4S)-2-hydroxy-1,7,7-trimethylbicyclo[2.2.1]hept-3-yl]-3-phenyl-2-propenamide with the diiodomethane/diethylzinc reagent proceeds with moderate diastereofacial selectivity only. However, the corresponding O-triisopropylsilyl-protected compound reacts with excellent but opposite diastereoselectivity the added diethyl tartrate has no influence on the stereoselectivity but only on the rate of the reaction. Similar effects are observed for the related cWo-derivatives of the amino alcohol auxiliary, which induces the opposite absolute configurations at the cyclopropane ring101. 

Preparative Methods for the synthesis of the parent and the 2-monoalkyl-substituted compounds, reduction of ethyl 3-chloropropionate with sodium-potassium alloy in the presence of chlorotrimethylsilane in ether. A recent modification using ultrasound irradiation is much more convenient and more widely applicable. Other substituted derivatives are prepared by cyclopropanation of alkyl silyl ketene acetals with the Furukawa reagent (diiodomethane/diethylzinc). ... 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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