Reaction with ylides

Among other olefins prepared in conventional ylide reactions with carbonyls are (68), (69), (70), and (71). ... 

Several of the stabilized ylide reactions with ketones also follow consistent patterns. Thus, a-hydroxy ketones afford ( )-enoates (Table 20, entries 5, 21, 22,44) (144), while most of the a-alkoxy derivatives favor the (Z)-isomers (entries 70, 74) (164). There is at least one exception in the a-alkoxy series where the ( )-enoate is favored (entry 77) (165), and there are several cases of puzzling selectivity with a,a -dialkoxy ketone substrates (entries 71,72,74) (164). As in many of the ketone Wittig entries, the observations are interesting and high selectivity is often possible. However, the results appear specific to a given class of substrates, and there are insufficient data to establish general trends. 

Further insight into structural details of possible TS depends on the correlation of stereochemical trends tabulated earlier and summarized in Table 22. Stabilized ylide reactions with simple aldehydes favor the trans-selective pathway. As discussed in connection with Table , the trans-disubstituted oxaphosphetanes are thermodynamically more stable than the cisdiastereomers, and the same preference should be felt in the late TS of... 

Freeman and Lloyd applied their now standard method to prepare diphenyltelluronium-2,3,4,5-tetraphenylcyclopentadienide (129). This first tellurium ylide was very weakly basic and would not undergo the typical ylide reactions with / -nitrobenzaldehyde or nitrosobenzene. 

Nitrogen Atom Transfer to Heteroatoms. PhI=NTs reacts with heteroatom lone pairs to generate ylides. Reaction with triphenylphosphine at 100 °C affords 69% of the phosphinimine (1) (eq 3). Likewise, PhI=NTs reacts with thioanisole to generate the iminosulfurane (2) in 49% yield (eq 4) and with dimethyl sulfoxide to quantitatively produce the sulfoximine (3) (eq 5). 

---