Ylids aldehydes

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

In the Wittig reaction an aldehyde or ketone is treated with a phosphorus ylid (also called a phosphorane) to give an alkene. Phosphorus ylids are usually prepared by treatment of a phosphonium salt with a base, and phosphonium salts are usually prepared from the phosphine and an alkyl halide (10-44) ... 

These ylids react readily with aldehydes, but slowly or not at all with ketones. In extreme cases (e.g., 41), the ylid does not react with ketones or aldehydes. Besides... 

Aldehydes and ketones can be converted to epoxides in good yields with the sulfur ylids dimethyloxosulfonium methylid (60) and dimethylsulfonium methylid (61). For most purposes, 60 is the reagent of choice, because 61 is much less... 

The generally accepted mechanism for the reaction between sulfur ylids and aldehydes or ketone is which is similar to that of the reaction of sulfur ylids with... 

Reaction between phosphorus ylids and aldehydes or ketones... 

Reaction of certain ylids with aldehydes (scoopy reactions)... 

Aldehyde (25) is piperonal (see p T 9) which we made from halide (31), the precursor of ylid (30), so either route is suitable. The route via (28) has been used. 

The double bond in (32) is trans since the Wittig used a stabilised ylid and an aldehyde. 

Dnstabilised ylids usually give more ais product with aldehydes. Muscature (36) is a house-fly pheromone used to bait traps and the obvious Wittig synthesis gives 85% aio and 15% truMy. ... 

Diene alcohol (38) is the pheromone of the codling moth, tlie creature responsible for the grubs in apples, and of the various possible disconnections (a) is best as it gives most simplification and a stabilised ylid (39) which will produce the requi red trans double bond. Allylic bromide (40) and aldehyde-ester (41) are available,... 

Disconnection (a2) leads to the industrial synthesis as the half aldehyde, hall ester (46) of fumarie acid (100% tpans) is available and the Wittig reaction with unstabilised ylid (45) gives 85% cis geometry in the new double bond. 

Ansuey If we disconnect the c-is double bond first (50a), we must use unstahilised ylid (51) and aldehyde (52) which can be made from stabilised ylid (53) and available half aldehyde, half ester (54). 

The obvious Vfittig disconnection gives stabilised ylid (5fi) and keto-aldehyde (57). We have used many such long-chain dicarbonyl compounds in this Chapter and they are mostly produced from available alkenes by oxidative cleavage (e.g. ozonolysis). In this case, cyclic alkene (58) is the right starting material, and this can be made from alcohol (59) by elimination,... 

Example Mali do (15, R=Pr-n) was used by Butenandt in his original synthesis of bombykol Cp iSf ) (16). Wittig disconnection of the tvans double bond requires cie allylic ylid (17), It is easier to use acetylenic ylid (18) and half aldehyde (19) in this step because el availability,... 

This is an extremely useful reaction for the synthesis of alkenes. It involves the addition of a phosphonium ylid, e.g. (136), also known as a phosphorane, to the carbonyl group of an aldehyde or ketone the ylid is indeed a carbanion having an adjacent hetero atom. Such species are generated by the reaction of an alkyl halide, RR CHX (137), on a trialkyl- or triaryl-phosphine (138)—very often Ph3P—to yield a phosphonium salt (139), followed by abstraction of a proton from it by a very strong base, e.g. PhLi ... 

Cis- and rranx-cyclopropane-1,2-diamines (both primary and secondary) react with a range of aldehydes, R CHO, to give pyrroles under very mild conditions. NMR has been used to identify the intermediates. The key steps involve ring expansion of the monoiminium ion (22), via an azomethine ylid (23), to yield a dihydropyrrolium ion (24). 

The formation of carbanions, according to Scheme 6, has been much studied but has proved to be of little preparative use. The benzyl anion, generated from benzyl-dimethylsulphonium tosylate, reacted with acrylonitrile but the addition product was formed in only low yield Similarly the reactive ylid formed by deprotonation of trimethylsulphonium salts has been cathodically generated and trapped by several aldehydes and ketones as well as ethyl maleate and fumarate examples are given in Scheme 7. For the best case (benzophenone), the epoxide was formed in 40%... 

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