Simmons-Smith conditions

Tab. 3.4 Cyclopropanation of the chiral enol ether 89 under Simmons-Smith conditions...

Enol esters have been used under Simmons-Smith conditions, and the prodncts are valuable precursors for cyclopropanols. Alternatively, the Uthinm enolate which can be obtained from the corresponding enol ester can be converted into the cyclopropanol derivative (equation 22). The direct cyclopropanation of zinc or lithinm enolates nsing... 

Those bis(trimethylsiloxy)alkenes resulting in the first step are reactive intermediates which can be converted into a variety of compounds — they give an easy access to many products in a one pot synthesis. For instance via bromination of 3,4-bis(trimethylsiloxy)-3-hexene (303) 2,5-dibromo-3,4-hexadione (307) can be achieved199 whereas l,2-bis(trimethylsiloxy)stilbene (304) yieldsbenzil (308)i99 Simmons-Smith conditions were applied, too, and 2,3-bis(trimethylsiloxy)-2-butene (290) gives l,2-dimethyl-l,2-bis(trimethylsiloxy)cyclopropane (306)2OO ... 

Cyclopropanation.1 The cyclopropanation of alkenes by this combination can be facilitated by sonication or by Ti(IV) chloride, but acetyl chloride is more effective. The effectiveness of this promotor may result from removal of traces of water and hydroxylic impurities. Yields using this expedient are generally higher (45-85%) than those obtained by the original Simmons-Smith conditions using diiodo-methane. 

Numerous methods or procedures have been reported for the activation of zinc5 and the cyclopropanation of the steroid derivatives 1 and of 2-cyclo-hexen-l-one serve as examples to illustrate two commonly used methods to activate the zinc dust (Equations 13.1 and 13.2, Protocols 1 and 2).67 The first reaction is a nice example of the directing ability and acceleration effect of an alcohol or of the zinc alkoxides under the Simmons-Smith conditions. 

Methylenation of some P-amino a,P-unsaturated esters or ketones under Simmons-Smith conditions is hampered by low activity of the olefins and formation of side products 107). 

Under Simmons-Smith conditions, bis-dihydropyran 566 was smoothly cyclo-propanated but 570 was also subject to transannular reactions under certain con-... 

Cyclopropanation of enol ethers, for example the conversion of 399 - 400, proceeds especially easy under Simmons-Smith conditions. This reaction offers additional options for the synthetic utilization of carbonyl compounds capable of forming enol ethers. Some of them will be considered later in this chapter (see Section 2.23.2). 

This method was utilized for the synthesis of the four stereoisomers of coronamic acid [17]. The ( )-allylic (3-D-glucopyranoside 3 was cyclopropanated under Simmons-Smith conditions at — 30°C with high diastereoselectivity (>100 1). The reaction of the corresponding (Z)-allylic... 

Reactions of halogen-stabilized carbenoids with imines have been carried out using prefoimed lithium species (e.g. equation 36), or via a carbenoid generated from diiodomethane utilizing zinc-copper couple (Simmons-Smith conditions). A stereospecific ring closure is observed after the addition of lithiodichloromethane to a benzaldimine (equation 37).The addition of lithiochloro(phenylsulfon-yl)methane to aromatic imines affords 2-phenylsulfonyl-substituted aziridines, which can be deproton-ated and alkylated in excellent yield (Scheme 20). 

The secondary marine metabolite (+)-acetoxycrenulide has unprecedented structural features which prompted L.A. Paquette et al. to embark on its total synthesis. The eight-membered carbocycle of the target was constructed via a Claisen rearrangement. The bicyclic p,y-unsaturated lactone was subjected to Simmons-Smith conditions, that delivered the cyclopropyl ring exclusively from the p-face of the molecule as a result of the predominant ground-state conformation. 

Alkenylalanes can dimerize to afford 1,3-butadienes (eq 30), and can be cyclopropanated under Simmons-Smith conditions to give cyclopropylalanes (eq 31), which can be used for further chemistry. 

Bis-(bromomethy1)mercury converts various olefins into cyclopropanes in high yields the reactions seem less sensitive to steric effects than the Simmons-Smith procedure. Methylcyclopropanes have been obtained in far higher yields than those afforded by Simmons-Smith conditions (45-96%) from olefins and 1,1-diiodoethane in the presence of diethyl2 inc. Similarly, carbenoid (as opposed to carbene) decomposition of aryldiazomethanes in the presence of olefins, zinc halides, and lithium halides, yields cyclopropanes in 40-90% yield. ... 

Many reactions result in a nearly simultaneous formation of a pair of o bonds. In some cases, a carbene is a transient intermediate. Carbene, iCH, is electron-deficient it lacks two electrons for a complete octet. Although there is no net charge and little or no dipole, it is highly electrophilic and will attack both jt and o electrons to form pairs of new bonds. The lack of specificity in this high reactivity renders iCH of little synthetic value, but selective cyclopropanation of alkenes may be accomplished using Simmons-Smith conditions (Eq. 7.36) [60], with a variety of methods available [61]. 

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