Iodonium ylides monocarbonyl

One of the most notable recent advances in iodonium ylide chemistry is the first demonstrable generation of iodonium enolates 44 formally derived from unactivated monocarbonyl compounds [197]. This was accomplished by the treatment of (Z)-jS-acetoxyvinyliodonium salts with lithium ethoxide, either in THF or in THF-DMSO (12 1) (Scheme 72). 

The unstable monocarbonyl iodonium ylides 437 can be generated from (Z)-(2-acetoxyvinyl)iodonium salts 436 by ester exchange reaction with lithium ethoxide in tetrahydrofuran (THF) at -78 °C (Scheme... 

Treatment of iodonium tetrafluoroborates 792 with triethylamine in methanol in the presence of triph-enylphosphine and aldehydes results in Wittig oleflnation to give products 793 (Scheme 3.313), which involves the intermediacy of monocarbonyl iodonium ylides 788 and their subsequent conversion into the respective phosphonium ylides upon the in situ reaction with PhsP [1089]. 

The interaction of monocarbonyl iodonium ylides, generated by the ester exchange of (Z)-(2-acetoxyvinyl)iodonium salts 792 with EtOLi, with organoboranes affords ketones 795, probably via intermediate formation of the hitherto unknown a-boryl ketones 794 (Scheme 3.314) [1090]. 

The reaction between Z-(2-acetoxyvinyl)iodonium bromides 1 and imines 3 in EtOLi, provides a route for the synthesis of 2-aeylaziridines 4 in good yields. It has been proposed fliat flie first step of the reaction consists in the in situ formation of a monocarbonyl iodonium ylide 2, that adds to the imine to give the eorre-sponding aziridines as cis. trans mixtures (Scheme 31.1). 

We can conclude that 2-acylaziridines 4 can be obtained from Z-(2-acetoxy-vinyl)iodonium bromides 1 and imines 3 in the presence of EtOLi. The reaction is a stepwise process. During the first step a monocarbonyl iodonium ylide 2 is formed by removal of the acetate group promoted by EtOLi. The second step consists in the nucleophilic attack of the ylide 2 to the imine C=N bond to yield a zwitterion intermediate (rate-determining step) that leads to the aziridine 4 by means of an intramolecular Sn2 reaction. The overall mechanism could be drawn as in Scheme 31.11. Although the aziridines 4 are obtained as cis trans mixtures, the stereochemical outcome of the reaction can be controlled by the reaction solvent and by the substituent on the nitrogen atom in the imines. 

Among some unstable phenyliodonium ylides the most interesting are those with a monocarbonyl carbanionic moiety which are formed from / -ace-toxyalkenyl(phenyl)iodonium precursors upon reaction with EtOLi (Scheme 52) [160]. These reagents are useful for the synthesis of a,/ -epoxy ketones and 2-acylaziridines. 

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