Benzyl bromide sulfide

Since cbiral sulfur ylides racemize rapidly, they are generally prepared in situ from chiral sulfides and halides. The first example of asymmetric epoxidation was reported in 1989, using camphor-derived chiral sulfonium ylides with moderate yields and ee (< 41%) Since then, much effort has been made in tbe asymmetric epoxidation using sucb a strategy without a significant breakthrough. In one example, the reaction between benzaldehyde and benzyl bromide in the presence of one equivalent of camphor-derived sulfide 47 furnished epoxide 48 in high diastereoselectivity (trans cis = 96 4) with moderate enantioselectivity in the case of the trans isomer (56% ee). ... 

Kinetic studies of various systems have been carried out as follows the reaction of 2,2 -dichlorodiethyl sulfide and of 2-chloroethyl ethyl sulfide with diethylenetriamine and triethylamine in 2-methoxyethanol ° the catalysed reactions of substituted phenols with epichlorohydrin the reactions of para-substituted benzyl bromides with isoquinoline under high pressure the reactions of O-alkylisoureas with OH-acidic compounds [the actual system was N, N -dicyclohexyl-0-(l-methylheptyl)isourea with acetic acid] and tlie ring opening of isatin in aqueous binary mixtures of methanol and acetonitrile cosol vents. 

Camphoryl sulfides ate mediators for one-step synthesis of optically active 1,2-diaryloxiranes from substituted benzaldehydes and benzylic bromides aided by potassium hydroxide (Scheme 5) (15). The reaction,... 

Benzophenanthrene Benzyl bromide Benzyl chloride Benzyl ethyl sulfide Benzyl iodide Benzyl methyl ketone Benzyl methyl sulfide Bicyclo[4.1.0]heptane Bicyclo[3.1.0]hexane... 

To a solution of chiral sulfide catalyst (9.5 mg, 0.05 mmol) and catechol (1 mg, 1 pmol) in t-BuOH (450 pL) was added the benzaldehyde (26 pL, 0.25 mmol), benzyl bromide (60 pL, 0.5 mmol) and n-Bu4NI (92 mg, 0.25 mmol). The resulting mixture was vigorously stirred at r.t. for 15 min (20-24 °C), and an aqueous solution of NaOH 28.5% (52 pL, 0.5 mmol, giving a 90 10 ratio of -BuOH water) was subsequently added. After 24 h of reaction, water (6 mL) was added, the two phases were separated, and the aqueous layer was extracted with diethyl ether (2x5 mL). The combined organic layers were dried over MgSC>4 and concentrated in vacuo. Purification by silica gel column chromatography afforded the two diastereoisomeric epoxides. 

A variation of the [C + C=N] pathway involves the addition of sulfur ylides to imines and this method has been effectively used to access a wide range of substituted aziridines under mild reaction conditions. Although high enantiomeric excesses can be achieved by using a chiral sulfur ylide (up to 98%), the m//rstepwise mechanism via a betaine intermediate . Sulfur ylides can be conveniently generated in situ from alkyl halides and chiral sulfides thus, benzyl bromide and tosyl imine in the presence of a camphor-derived chiral sulfide mediator provide aziridine 4 in practically quantitative yield as a 3 1 mixture of /Z-isomers and in 92% ee (A-isomer) (Scheme 8) <2001TL5451>. 

The same alkyl thiocarbamates 95 can be prepared in 35-72% yield by reaction with disulfides and with carbon disulfide followed by alkylation with alkyl halides100. When carbonyl sulfide was used as electrophile, lithium /V,/V-dialkyldioxamates were formed, which after reaction with benzyl bromide gave thiooxamates 96 in 37-56% yield100. 

The phenyl-substituted sulfide 91 (R = Ph) was used for the synthesis of various a-disubstituted phosphepines 93 via sequential deprotonation steps with Bu Li and subsequent treatment with trimethylsilyl chloride (TMS-C1), alkyl iodide, or benzyl bromide <2005TA3416>. 

Sulfur ylides, derived from benzyl bromides and an optically active alkyl sulfide, undergo base-promoted reactions with aryl aldehydes to produce optically active 1,2-diatyl epoxides.The reaction is illustrated by equation (17) and produces epoxides with optical purities in the range of 28-47% ee. The bicyclic sulfide shown in equation (17) was derived from (-t-)-camphor8ulfonic acid and produces the (RiO-enantiomer of the epoxide in excess. 

The successful example of catalytic asymmetric chiral sulfonium epoxidation was reported with enantiomeric excess (43%) of trans-stilbene oxide (3.71) by the reaction of 4-chlorobenzaldehyde with benzyl bromide in acetonitrile at room temperature by using 0.5 equiv. of optically active sulfide 3.70 (with exo-OH group). Powdered KOH was used as a base. f... 

Aziridines can also be synthesized enantioselectively from imines and alkyl halides using a camphor-derived chiral sulfide mediator 640 in a one-pot procedure via the imino Corey-Chaykovsky reaction. Thus, benzyl bromide 641 and tosyl imine 642 provide aziridine 643 in practically quantitative yield as a 3 1 mixture of ( /Z)-isomers and in 92% ee ((i4)-isomer) (Scheme 157). An electron-withdrawing substituent on the imine nitrogen is necessary to activate the 7t-system for nucleophilic attack <2001TL5451>. 

Although benzylic sulfides will be treated later in a separate section, the synthesis of zearalenone gives the first opportunity to mention their synthetic use. The introduction of sulfur to build the aromatic part of zearalenone was done in two different ways displacement of a benzylic bromide by benzenethiol or reaction of diphenyl disulfide with benzylic carbanion (Scheme 11). 

Hart assembled olefin 109 convergently from benzyl bromide 106 by taking advantage of the Ramberg-Backlund reaction.59 As depicted below, the Sn2 displacement of benzyl bromide 106 with thiol 107 led to sulfide 108. Oxidation of 108 to the sulfone, followed by the Myers modification delivered alkene 109, an intermediate for the synthesis of C-aryl glycosides related to chrysomycins. 

Bromo-5-methoxy-benzyl bromide 2-Bromo-5-medioxybenzyl mediyl sulfide... 

An alternative approach to the ylide methodology, appealing in its simplicity, has been developed by Metzner and co-workers <01JOC5620>. In this protocol, the sulfur ylide is generated in situ by the reaction of chiral sulfide 48 with, for example, benzyl bromide, which provides the ylide after deprotonation with NaOH. In this way, furaldehyde (49) was converted to furyl epoxide 51 in a one-pot reaction in 89% yield and 93% ee. 

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