Arsonium ylides synthesis

An Australian worker has described recently a novel synthesis of highly functionalised cyclopropanes which proceeds in moderate yield, and is illustrated by the following example. Addition of the 2//-pyran-5-carboxylate 1 to the arsonium ylide 2 in THF at 0°C gave two trans-diastereomers 3 in 64% yield. 

Arsonium ylides. Semistabilized allylic arsonium ylides are generally not useful in synthesis because they react with carbonyl compounds to form mixtures of epoxides and alkenes. Unexpectedly, the reaction of the semistabilized ylide triphenylarsonium... 

Dialkylamino-aryloxosulfonium alkylides may be employed for enantioselective epoxidation if the ylide with its chiral sulfur center is resolved into its enantiomeric form, " An enantioselective oxirane is obtained by means of a chiral phase-transfer catalyzed procedure with dimethylsulfonium methylide. The utilization of arsonium ylides was reported some time ago. ° A highly stereoselective synthesis of trans-epoxides with triphenylarsonium ethylide has recently been described.Optically active arsonium ylide has been used in the asymmetric synthesis of diaryloxiranes. ... 

Chiral arsonium ylides containing the benzylidene group react with aromatic aldehydes to produce trans-2,3-diaryloxiranes with optical purities of up to 41%. The degree of asymmetric induction depends upon the nature of the substituents on the ylide, the substrate, and upon the reaction conditions. For the variety of arsonium ylides investigated, however, the yields of recovered optically active arsines were almost quantitative with complete retention of configuration at arsenic in each case. Thus, apart from the value of stereoselective benzylidene transfer for the asymmetric synthesis of trans-2,3-diaryl oxiranes, the reaction provides the cleanest route to the recovery of optically active arsines from resolved benzylarsonium salts (see Section III.B.5). The mechanism of the reaction, which must take into account the exclusive formation of trans-diaryloxiranes, is believed to occur via the stereoselective decomposition of a pair of (R, S )-betaines (Scheme 16). 

The synthesis of the arsonium ylides most commonly involves deprotonation of arsonium salts utilizing a variety of bases. Simple arsonium salts are available via direct alkylation of triphenylarsine, but more highly substituted compounds require specialized methods. These include the use of highly electrophilic triflate salts, alkylation of triphenylarsonium methylide, and double alkylation of lithiodiphenyl-arsine. For some purposes, formation of the tetrafluoroborate salts is desirable and can be effected in good yield by cation exchange. ... 

The synthesis of arsonium ylides 384 from diazocyclopentadienes 383 and tri-phenylarsine has been reexamined with respect to the efficiency of various copper-containing catalysts Whereas copper bronze gave only ca. 55 % of ylide, yields over 80% were provided by the use of Ou(II) complexes of p-diketonates derived from acetylacetone, 3-methylacetylacetone, benzoylacetone or dibenzoylmethane, as well as by bis[4-(phenylimino)-2-pentanonato-N,0-]copper(II) and Cu(II) acetate, all used in boiling benzene. The sterically more demanding complex bis(dipivaloyl-methanato)copper(II) as well as dichlorodipyridinecopper(II) proved less efficient. CopperfTI) tartrate, the dibenzo-14-crown 6/copper complex and furthermore the acetylacetonate complexes of Co, Ni, Pt and Zn were totally ineffective. When 383a was decomposed by Cu(acac)2 in the presence of pyridine or thioanisole. 

Ring synthesis from nonheterocyclic compounds Arsonium ylides in synthesis of heterocycles 05T1385. 

Arsenic and Bismuth.—A partial asymmetric synthesis of diaryloxirans is dependent on optically active arsonium ylides (89). Yields are high, but optical... 

Scheme 37.14 Synthesis of functionalized cyclopropanes through the [2+1] cycloaddition of enals and arsonium ylides.

It is well known that aziridination with allylic ylides is difficult, due to the low reactivity of imines - relative to carbonyl compounds - towards ylide attack, although imines do react with highly reactive sulfur ylides such as Me2S+-CH2-. Dai and coworkers found aziridination with allylic ylides to be possible when the activated imines 22 were treated with allylic sulfonium salts 23 under phase-transfer conditions (Scheme 2.8) [15]. Although the stereoselectivities of the reaction were low, this was the first example of efficient preparation of vinylaziridines by an ylide route. Similar results were obtained with use of arsonium or telluronium salts [16]. The stereoselectivity of aziridination was improved by use of imines activated by a phosphinoyl group [17]. The same group also reported a catalytic sulfonium ylide-mediated aziridination to produce (2-phenylvinyl)aziridines, by treatment of arylsulfonylimines with cinnamyl bromide in the presence of solid K2C03 and catalytic dimethyl sulfide in MeCN [18]. Recently, the synthesis of 3-alkyl-2-vinyl-aziridines by extension of Dai s work was reported [19]. 

Arsenic, Antimony, and Bismuth.- (Diphenylarsino)methyl-lithium (203) has been prepared by either halogen-lithium or tin-lithium exchange from (204) or (205) respectively. Interestingly the reactivity of (203) depends on the method of preparation used, although the reasons for this are not known. A stereoselective synthesis of JE-a, -unsaturated aldehydes has been achieved by reacting aldehydes with the arsonium salt (206) in the presence of a weak base. The ylide derived from (206) shows a reasonable... 

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