Ylides, with benzaldehydes

The first report of such effects was in a study of the reactions of a series of tris(p-substituted phenyl)arsonium ylides with benzaldehyde all these ylides gave epoxides in high yield save for the tris(p-dimethylamino) compound, which gave instead the trans-alkene L In further experiments replacement of a triphenylarsonium group by a tris(p-methoxyphenyl)arsonium group was found to have little effect on the ratio of products and inclusion of the arsenic atom in a strained ring also had no effect. ... 

The results of the reactions of the ylides with benzaldehyde in THF solution under a variety of conditions are given in Table I. 

Terada and Kishida have reported unusual reactions of a series of alkynyldimethylsulphonium ylides with benzaldehydes. The stabilized ylide (35) resulted from reaction of benzaldehydes with the sulphonium salt (36) in the presence of sodium hydride. Although the mechanism... 

The synthesis of stabilized phosphorus ylides via multicomponent reactions and their synthetic applications have been reviewed. The Wittig reaction products of keto-stabilized ylides with orf/io-substituted benzaldehydes have been found to show significantly higher than expected Z-alkene content (up to 50%) compared to analogous reactions of the same ylides with benzaldehyde itself. A cooperative effect is seen whereby the unusual Z-content is further augmented if the ylide bears greater steric... 

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). ... 

In an attempt to prepare sulfonium-ylide polymer, Tani-moto and coworkers [57,58] carried out the reaction of a sulfonium salt polymer with benzaldehyde in the presence of a base and obtained styrene oxide. The reaction was considered to process via a ylide polymer formation (Scheme 24), which may be unstable and has not been isolated. 

The aldehyde structures and the tosylhydrazone salts were varied in an extensive study of scope and limitations, with use of both achiral and chiral sulfur ylides [73]. Aromatic aldehydes were excellent substrates in the reaction with benzaldehyde-derived ylides, whereas aliphatic aldehydes gave moderate yields and transxis ratios. 

The "one-pot domino reaction" of A/-benzylaniline with benzaldehyde in refluxing toluene results in a mixture of oxazolidines via a transient azomethine ylide (Scheme 14) <96S367>. The 2-benzoyloxazolidine 69 rearranges spontaneously to the oxazine 70 <96JHC1271>. The ring-closure of derivatives 71 (R = H or Me) of (f )-phenylglycinol to oxazolidin-2-ones... 

When the phosphonium ylide 81 is reacted with zinc amide, the corresponding a-zincated phosphorus yUde is formed. Thermally unstable, it evolves almost quantitatively to zincatacyclobutane 82 which in presence of pyridine leads to the formation of the zincataphosphoniaindane 83. In order to explain this unprecedented cyclometallation reaction, a mechanism is proposed involving a low coordinated zinc center. The new product, reacted with benzaldehyde leads to the diphenylallene 84 (Scheme 27) [106-108]. 

In addition to nitrones, azomethine ylides are also valuable 1,3-dipoles for five-membered heterocycles [415], which have found useful applications in the synthesis of for example, alkaloids [416]. Again, the groups of both Grigg [417] and Risch [418] have contributed to this field. As reported by the latter group, the treatment of secondary amines 2-824 with benzaldehyde and an appropriate dipolarophile leads to the formation of either substituted pyrrolidines 2-823, 2-825 and 2-826 or oxa-zolidines 2-828 with the 1,3-dipole 2-827 as intermediate (Scheme 2.184). However, the yields and the diastereoselectivities are not always satisfactory. 

The synthesis of the planar, tricyclic- A5-phosphorin (179) has been described.161 It reacts with methyl iodide to give the salt (180) as a mixture of stereoisomers, and is in equilibrium with the ylide (181), which reacts with benzaldehyde to give the oxide (182). 

After these results had established the feasibility of generating and utilizing a carbohydrate phosphorane, the two systems that had been reported earlier were examined in order to determine if similar conditions would allow them to undergo the Wittig reaction. The ylide derived from phosphonium salt I condensed with both benz-aldehyde and U-chlorobenzaldehyde to produce good yields of olefinic products Villa and Vlllb. The ylide derived from phosphonium salt II also was successfully condensed with benzaldehyde, but the yield of IX was only 30 , presumably because of its extremely poor solubility even in an HMPA-THF solvent mixture. Both of these systems supported the tenet that it was possible to use unstabilized carbohydrate phosphoranes if the conditions are proper and if the g-oxygen is attached to the carbohydrate through another set of bonds. 

Enders et al. (53) reported the use of chiral l,3-dioxan-5-ylamines in condensation reactions with aromatic aldehydes to form ylides in situ, which underwent thermal cycloaddition reactions with excellent yields. Treatment of 193 with benzaldehyde or p-fluorobenzaldehyde in the presence of excess dimethyl fumarate or fumaronitrile gave rise to the expected adducts in 85% yield with a >96% diastereomeric excess. For nitriles (R = CN), the endo/exo selectivity was higher at 70 30 than for the esters (R = C02Me) at 55 45 (Scheme 3.56). 

The chiral dipolarophiles of Garners and Dogan, which were derived from Oppolzer s sultam, have been previously discussed in Section 3.2.1 and, in an extension to these results, the sultam moiety was used as the stereodirecting unit in enantiopure azomethine ylides (56). The ylides were generated either by thermo-lytic opening of N-substituted aziridines or by the condensation of the amine functionality with benzaldehyde followed by tautomerism. These precursors were derived from the known (+)-A-propenoylbornane-2,10-sultam. Subsequent trapping of the ylides with A-phenylmaleimide furnished the cycloaddition products shown in Schemes 3.60 and 3.61. 

Padwa et al. (44) studied the diazo-decomposition of 119 and found that the cyclic ylide 120 could be trapped by a variety of heterodipolarophiles such as ethyl cyanoacetate (Mander s reagent) to provide aminal 121 or with benzaldehyde to generate the bicyclic acetal 122. In both cases, only a single isomer was formed, with the regiochemistry easily predicted from frontier orbital considerations. Nair et al. (45) were able to employ the highly functionalized o-quinone 125 for the trapping of carbonyl ylide 124 to provide the highly complex cycloadduct 126 in 76% yield. 

Enders et al. (96) recently described the application of the chiral azomethine precursor 61 (Scheme 12.21). The azomethine ylide was formed in situ by heating with different benzaldehydes. The reactions of four different azomethine ylides with A-phenyl maleimide led to the formation of endo-62 and exo-62 in ratios of 2 1 in very high yields. The diastereofacial selectivity was estimated to be >96% de for both products, since no other diastereomers were observed by proton nuclear magnetic resonance ( H NMR) spectroscopy. 

Nesmeyanov et al. (74, 75) reported the reaction of acetylmethylene triphenylarsorane with benzaldehyde. Huang et al. (50) found that this ylide reacted with ketones as well as aldehydes in moderate to excellent yields. 

Only a limited number of examples have been reported. The reactivity of sulfonium ylide 98a, prepared by the reaction of thiepine 96 and dimethyl diazomalonate (Section 13.03.6.1), was examined <20060BC2218>. The reactivity of the stabilized sulfonium ylide 98a was restricted to the highly reactive Michael acceptor, tetracya-noethylene 152 (the ylide failed to react with benzaldehyde or dicyanoethylene). Reaction of ylide 98a with tetracyanoethylene 152 led to the consumption of the ylide 98a (Equation 22). Thiepine 96 was produced in the reaction and the formation of cyclopropane 153 was suggested. 

Aryl-stabilized ammonium ylides from deprotonation of (95 X = CH, N) react with benzaldehyde to give epoxides (96).274 The diastereoselectivity is highly sensitive to the nature of the amine and the ylide substituent, e.g. it reaches 99 1 trans. cis... 

The ring expansion of the carbene dioxolane 208 occurred in the presence of Rh(n) catalyst. The reaction proceeded presumably via the intermediate ylide 209, which was subjected to the reaction with benzaldehyde in the presence of Lewis acid to give a mixture of the dioxocine 210, as the major product, as well as dioxocane 211 (Scheme 24) <2003JOC10040>. Compounds 210 and 211 were separated and the yy -conformation of 210 was determined by X-ray crystallographic analysis. The stereochemistry of 211 was also established by X-ray crystallography. 

Indeed, in diethyl ether, lithium dimethylcuprate usually reacts with the a-enone group to give a methyl-substituted bromo ketone. Addition of hexamethylphosphoric triamide (HMPT), however, slows down this reaction to such an extent that displacement of the bromo substituent takes place [698], Another remarkable example of the influence of HMPT on chemoselectivity is the reaction of an arsonium ylide, Ph3As= CH-CH=CH-Ph, with benzaldehyde in tetrahydrofuran solution, yielding either an epoxide (in THE) or an alkene (in THF/HMPT) [699],... 

Trost showed that the sulfur ylide 3.68 prepared by the deprotonation of 3.67 with n-butlyllithium (n-BuLi) on reaction with benzaldehyde under the same reaction conditions gave styrene oxide 3.69 as a racemic mixture. 

Johnson et al. were the first to prepare enantiomerically pure aminosulfoxonium ylide 3.73 from 3.72, which on reaction with benzaldehyde gave (P)-styrene oxide (3.69) in 20% ee. The reaction of aminosulfoxonium ylide 3.74 with heptaldehyde gave the corresponding epoxide 3.75 with opposite enantioselectivity (39% ee, S) as expected. 

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