Allyl telluronium salts

Intensive investigations have been devoted to the synthesis of vinyl cyclopropanes by using allylic telluronium salts. Vinyl cyclopropanes are important compounds as versatile synthetic intermediates and as participants in the structure of several biologically active natural compounds. ... 

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]. 

Thus, allyl telluronium ylides generated in situ from the corresponding telluronium salts in the presence of Li salts react with a,)3-unsaturated esters and amides to afford trans-2-vinyl-/rany-3-substituted cyclopropyl compounds in high yieds. 

The reaction of aUyl telluronium salts with phenols in the presence of solid NaOH in THF leads to allylic ethers in excellent yields. ... 

To a mixture of a,/ -unsaturated compound (0.25 mmol), CS2CO3 (0.27 mmol), and telluronium salt catalyst (0.05 mmol) in THF (0.5 mL) was added trimethyl-silyl allylic bromide (0.5 mmol) in portions over 8 h at reflux. When the reaction was complete (monitored by GC), the resulting mixture was filtered through short silica gel column and washed with ethyl acetate. The filtrate was concentrated, and the residue was purified by FC to afford the desired product. 

Dialkyl telluriums, diaryl telluriums, and alkyl aryl telluriums are converted to triorgano telluronium salts on reaction with alkyl halides. These alkylations proceed easily with methyl, ethyl, and propyl iodide4, allyl bromide5,6, cyclohexyl iodide7, ethyl bromoace-tate8, and even bromobenzene and iodobenzene4,8. 

Related cyclopropanations have also been reported using sulfonium and telluronium ylides as intermediates. In particular, the cyclopropanation of enones has been carried out employing an allyl bromide as the cyclopropa-nating reagent and sulfonium and telluronium salts 134 and 135 as pre-catalysts (Scheme 7.84). These species, in the presence of a base, generated the corresponding ylide which underwent the cascade Michael/intramolecular nucleophilic substitution and it is in this second step that the real catalytically active species is released, able to interact with another molecule of the allyl bromide and thus regenerating the sulfonium or telluronium salts pre-catalysts, which can afterwards continue in the catalytic cycle. The substitution at the... 

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