Ylides benzaldehyde reaction

The tandem carbonyl ylide/cycloaddition reaction is also observed when crotonaldehyde or acetone is used instead of benzaldehyde (dimethyl fumarate as dipolarophile), whereas with cyclohexanone, an enol ether derived from the carbonyl ylide is isolated [19] (Scheme 9). 

Recently, several sulfides with a bicyclo[3.2.1] framework have been developed for the ylide epoxidation reaction. In 2008, Metzner and coworkers prepared several bridged sulfides starting from (R)-carvone, which were then evaluated in the epoxidation of benzaldehyde with benzyl bromide (Scheme 20.8). Sulfide 12 was found to be the most enantioselective, delivering the desired trans epoxide in 54% yield and 84% ee in 4 days. Sulfide 15, which was prepared from 12 by reacting with PhLi followed by dehydration, is much more reactive than 12, providing 80% yield in one day but the enantioselectivity was lower (55% ee) [19]. 

An unusual 1,4-oxathian synthesis, the formation of (174) in 12% yield, was observed in the phase-transfer-catalysed generation of dimethyloxosulphonium methylide and its reaction with benzaldehyde. A possible pathway to (174) involves protonation and dehydration of the initial ylide-benzaldehyde adduct to give (175). Ylide formation at a methyl... 

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). ... 

The free acid analogue of the antipsoriatic agent etretinate (103) is prepared in substantially the same way as the parent compound. Thus, the aldehyde group in 98 is converted finally to the pho.sphonate (101) by sequential reduction (99), conversion to the chloride (100), and finally reaction with triethyl phosphite. Condensation of the ylide from 101 with the benzaldehyde 102 gives etretinate (103) saponification affords acitretin (104) [25]. 

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]. 

Sulfur ylides are a classic reagent for the conversion of carbonyl compounds to epoxides. Chiral camphor-derived sulfur ylides have been used in the enantioselective synthesis of epoxy-amides <06JA2105>. Reaction of sulfonium salt 12 with an aldehyde and base provides the epoxide 13 in generally excellent yields. While the yield of the reaction was quite good across a variety of R groups, the enantioselectivity was variable. For example benzaldehyde provides 13 (R = Ph) in 97% ee while isobutyraldehyde provides 13 (R = i-Pr) with only 10% ee. These epoxy amides could be converted to a number of epoxide-opened... 

Copper(I) catalyzed decomposition of iodonium ylide 12 in the presence of a large excess of benzaldehyde results in the formation of oxirane 14. The reaction probably occurs via carbonyl ylide 13, followed by the ring closure [92JCS(P1)2837],... 

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). 

Carbonyl ylides can be viewed as an adduct between a carbonyl group and a carbene and, in fact, some ylides have been prepared this way (see above). The application of carbonyl ylides to the synthesis of complex natural products has been greatly advanced by the finding that stabilized carbenoids can be generated by the decomposition of ot-diazocarbonyl compounds with copper and rhodium complexes. The metallocarbenoids formed by this method are highly electrophilic on carbon and readily add nucleophiles such as the oxygen of many carbonyl derivatives to form carbonyl ylides. This type of reaction is in fact quite old with the first report being the addition of diazomalonate and benzaldehyde (33,34). 

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