Nitrogen ylides rearrangement

With the aid of a nitrogen ylide rearrangement, it is possible to transform an allylic secondary amine to an unsaturated carbonyl system, in certain circumstances with transfer of chirality (Scheme 53). ... 

Mechanistically the rearrangement is formulated to proceed via an intermediate radical-pair or ion-pair. In either case the initial step is the formation of a nitrogen-ylide 2 by deprotonation of the ammonium species with a strong base. The abstraction of a proton from the a-carbon is facilitated by an electron-withdrawing group Z—e.g. an ester, keto or phenyl group ... 

Nitrogen ylides are also known to undergo [1,2]- (Stevens) and [2,3]-rearrangements. The Stevens rearrangement occurs through a mechanism that involves homolytic cleavage... 

The addition of diazomethane to cyclobutanones results in a convenient expansion to cyclopen-tanones. With few exceptions, the rearrangement of the intermediate nitrogen ylide is highly regioselcctive, only one product is generally isolated, particularly in cases where both substituted cyclobutanones and substituted diazomethanes are used. Typical examples are shown in Tabic 6 further examples can be found in refs 57, 59. 61 -63 and 65-68. 

A synthesis of a-( trifluoromcthyl)-a-amino esters 5 has been developed based on the [1,2] Stevens rearrangement of nitrogen ylides 4, obtained by the transition-metal-calalyzed decomposition of methyl 2-diazo-3,3,3-trifluoropropanoate (3) in the presence of tertiary amines.2... 

A valuable part of the [2,3]-sigmatropic rearrangement of ammonium ylides is the fact that stereochemical information can be transferred. For example, Kaiser and co-workers stereoselectively alkylated the C-6 position of penicillin using the nitrogen ylide 46 derived from lactam 45.28 Quatemization of 45 with allyl bromide followed by ylide generation using sodium hydride effected the [2,3]-rearrangement. This resulted in the exclusive formation of P-lactam 47 in 75% yield. 

Propargylic groups are also known to participate in [2,3]-sigmatropic rearrangements and lead to the isolation of allenes as the major products. For example, the nitrogen ylide 65 was formed by treating the corresponding ammonium salt with NaH in DMSO afforded allene 66 in 86%... 

The nitrogen ylides (3.60) are formed as intermediates in the Sommelet rearrangement ". The method is used for the conversion of the tetraalkylammonium halides 3.59 (having hydrogen in an a-position to N) into tertiary aromatic amines 3.61 (Scheme 3.25). 

Equatorial attack was reported for the rearrangements of sulfonium and nitrogen ylides in the conforma-tionally fixed Bu -substituted cyclohexanes (152 equation 43) and (153 equation 44), respectively. 

Treatment of the nitrogen ylides 74 (R1 = Me, Ph R2, R3 = alkyl) with sulphur in hot benzene gives the amines 75 ( 30% yield) (Eq. (11)). A mechanism for this Dimroth-type rearrangement has been proposed. The structure of the product 75 (R1 = Ph, R2 = R3 = Me) has been confirmed by X-ray crystallography (95JOMC127). 

The (cyclopropylamino)carbene complex 15 reacted with diphenylalkyne to give a nitrogen ylide, which was converted via thermal A -cyclopropyl to C-cyclopropyl rearrangement and decomplexation to a cyclopropyl-substituted lactam. 

In contrast to the nitrogen ylide, alkylidenetriphenylphosphines give air-stable crystalline compounds (104) with 1-boraadamantane (5) (Scheme 39) <84JOM(260)17>. Adducts (104) rearrange to 4-alkyl-3-borahomoadamantane series (105) under reflux in chlorobenzene these form complexes (106). 

Sommelet-Hauser rearrangement of the nitrogen ylide formed upon desilylation of oxazolinium derivatives affords benzoxazocines (67) and/or their putative tautomers (84) in low to modest yield... 

Geometrical trans to cis isomerization of 3,3 -, 4,4 -, and 5,5 -disubstituted 2,2 -diphenoquinones has been studied by computational methods.The double bond isomerization of butene-catalysed l-ethyl-3-methyl-imidazolium chloride ionic liquid has been similarly examined and stepwise isomerization is suggested.The reaction of l,2-di(l-adamantyl)-2-thioxoethanone with diazomethane and 2-diazopropane gave 2-acylthiiranes via 2 - - 3-cycloaddition, elimination of nitrogen, and 1,3-dipolar electrocyclization of the intermediate acyl-substituted thiocarbonyl ylides. Rearrangement of pyrimidine-5-carboxylic acids esters to 5-acylpyrimidones does not occur in the examples studied and a [l,4]-phospho-Fries rearrangement has been reported. ... 

Although nitrogen ylides have been extensively used in organic transformations, especially those concerning the formation of nitrogen heterocycles,not many references are available for the use aza-sulfonium ylides and the Sommelet-Hauser rearrangement in the synthesis of indole derivatives. 

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