Ylides 1,2 -Stevens rearrangements

The addition of /i-toluenesulfmate to the silyl ether of l-hydroxybut-3-yn-4-yl(phenyl)iodonium triflate triggers a sequence of reactions that ultimately delivers 2-substituted-3-(/i-toluenesulfonyl)dihydrofuran products in variable yields (Scheme 31). A putative 1,2-group shift within an unsaturated oxonium ylide (Stevens rearrangement) accounts for the oxygen-to-carbon transfer of the ether substituent <2000JOC8659>. 

The amine a-anions (38a-c) failed to rearrange under conditions employed for the analogous ethers. The corresponding ammonium salts, on the other hand, readily isomerize via the derived ylides (Stevens rearrangement) in a process analogous to the 1,2-Wittig rearrangement. ... 

Scheme 2.53 [2,3]-Stevens rearrangement of a vinylaziridine-derived ammonium ylide 219.

The aza-[2,3]-Wittig rearrangement of a vinylaziridine-derived quaternary azir-idinium ylide (i.e., [2,3]-Stevens rearrangement) has recently been reported (Scheme 2.53) [86], The aziridinium ylide 219, generated by the intramolecular reaction of a copper carbenoid tethered to a vinylaziridine, underwent a [2,3]-Ste-vens rearrangement to furnish the bicydic amine 220 with the indolizidine skeleton. 

The key step in the total synthesis of (—)-epilupinine 253 involved the ring expansion of a proline-derived spirocyclic ammonium ylide to give 252 through a [1,2] Stevens rearrangement, as shown in Scheme 51 <1997T16565>. 

Muroni et al. have reported a tandem metallocarbenoid/ylide/[l,2]-Stevens rearrangement <2004TA2609>. The azoniaspirocycle ylide 5 is formed by trapping of the metallocarbene precursor (Equation 14). Heating the ylide in toluene then gave indolizidinone 55 as a single diastereoisomer. 

The CJS insertion reaction was suppressed completely upon catalytic decomposition of diazoketones 361, where the sulfur substituent was alkyl, acyl or thioacyl. It is presumed that sulfonium ylides occur as intermediates which give cepham (or cephem) derivatives in all cases270,343) rather than products of a Stevens rearrangement. 

At low temperatures cyclopropenones and enamines or ketene acetals were shown to yield 2-azonia-bicyclo(3,l, 0)hex-3-enolates-3 (371, X=0), which can be isomerized thermally to penta-2,4-diene amides(372, X=0). At elevated temperatures the amides were found to be the principal products arising from C-N-insertion 237) (insertion of the cyclopropenone three-carbon unit into the C-N bond of the enamine). These were accompanied in some cases by 3-aminoenones 373 arising from C-C-insertion 237) (insertion of the cyclopropenone into the C-C double bond of the enamine) and a-amino cyclopentenones 375 formed by Stevens rearrangement of the ylide 369 and cyclopentenones 374 ( condensation 237)). 

Ammonium ylides can isomerize to (1,2) rearrangement products (Stevens rearrangement) or to (2,3) shift products (Sommelet-Hauser sigmatropic rearrangement) when allyl or benzyl are located on the nitrogen atom. A strong microwave effect is noticed (Eq. 66) [116]. 

A ring enlargement process was used effectively to access the enantiopure pyrrolo [ 1,4]oxazepine-9a(7//)-carboxylate derivatives 142 and 143. The sequence involved copper (Il)-catalysed decomposition of an a-diazocarbonyl derivative attached to a chiral morpholinone, and a carbenoid, spiro-[5,6]-ammonium ylide, Stevens [1,2] rearrangement sequence. The Stevens and related rearrangements have considerable further potential for novel heterocyclic syntheses <00TA3449>. 

Photolysis or thermolysis of heteroatom-substituted chromium carbene complexes can lead to the formation of ketene-like intermediates (cf. Sections 2.2.3 and 2.2.5). The reaction of these intermediates with tertiary amines can yield ammonium ylides, which can undergo Stevens rearrangement [294,365,366] (see also Entry 6, Table 2.14 and Experimental Procedure 2.2.1). This reaction sequence has been used to prepare pyrrolidones and other nitrogen-containing heterocycles. Examples of such reactions are given in Figure 2.31 and Table 2.21. 

Tertiary amines can react with electrophilic carbene complexes to yield ammonium ylides which usually undergo Stevens rearrangement (Figure 4.8) leading to products of a formal carbene C-N bond insertion. 

Fig. 4.8. Formation and Stevens rearrangement of ammonium ylides from acceptor-substituted carbene complexes.

Experimental Procedure 4.2.5. Ammonium Ylide Formation and Stevens Rearrangement Diethyl 2-Benzyl-2- [(ethoxycarbonyl)mefiryl](methyI)amino malo-nate [1241]... 

As a similar transformation of aza-[2,3]-Wittig rearrangement, a [2,3]-Stevens rearrangement to 126 of the A-silylated ylide derived from A-crotylglycine ester (125) was reported (equation 75) . 

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... 

Naidu, B.N. The Stevens Rearrangement of Ammonium Ylides and Its Applications to the Synthesis of Azaheterocycles, a-Amino Add Derivatives and Optically Active (-)-Epilupi-nine Ph.D. Dissertation, University of Utah,... 

Common reactions of the ylide include (i) [2,3]-sigmatropic rearrangement of allylic, propargylic, and allenic ylides (ii) [l,2]-shift (Stevens rearrangement) (iii) 1,3-dipolar cycloaddition of the ylide generated from carbonyl compounds or imines with dipolarophiles, usually G=G or C=C bonds and (iv) nucleophilic addition/elimination, leading to the formation of epoxides or cyclopropanes (Figure 2). 

The other major reaction pathway for oxonium ylide is [l,2]-shift (Stevens rearrangement). Compared with [2,3]-sigmatropic rearrangement, which is an orbital symmetry-allowed concerted process, the [l,2]-shift has higher activation barrier, [1,2]-Shift is generally considered as stepwise process with radical pair as possible intermediates. 

Van den Berg et al. suggested an intramolecular Stevens rearrangement of the oxo-nium ylide to ethyl methyl ether to interpret carbon-carbon bond formation463 [Eq. (3.55)]. Olah and coworkers, however, provided evidence (based on isotopic labeling studies) that the oxonium ylide undergoes intermolecular methylation to ethyl dimethyloxonium ion [Eq. (3.56)] instead of Stevens rearrangement 447... 

Other heterocyclic tertiary amines show a different behavior. Tertiary amines have been used as catalysts in dichlorocyclopropanation of olefins they probably give an ammonium ylide as the first step in the catalytic cycle.262 These ylides are usually unstable and undergo a variety of transformations such as the Stevens rearrangement and the Hoffmann elimination. 

Boekelheide and his collaborators [407] have described a two-step sequence for transforming sulfide linkages to carbon-carbon double bonds — Stevens rearrangement of sulfur ylides and Hofmann elimination — which they found particularly useful for the synthesis of cyclophane derivatives, such as the [2.2]metaparacyclophane-l,9-diene shown. The Ramberg-Backlund rearrangement (see Section 4.3.2) was unsatisfactory for such highly strained molecules. 

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... 

Although, in principle, any arsonium ylide could be prepared via the slat method as demonstrated above, attempts to prepare a ylide from dimethyldibenzylarsonium salt (4) with ethereal phenyllithium failed. The product of the reaction after quenching with water was stilbene (5). Apparently, a Stevens rearrangement occurred during the reaction (101). 

Thiopyranylindole 236 underwent ylide-derived Stevens rearrangements when exposed to malonate and cr-ketoester carbenoids and resulted in a one-carbon ring expansion reaction to lead to thiepines <2005JOC746>. Thus, reaction of thiopyranylindole 236 with dimethyl diazomalonate and /-butyl diazoacetylacetate in the presence... 

Recent advances in the Stevens rearrangement of ammonium ylides have been reviewed in terms of application to the synthesis of alkaloid natural products.147... 

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