Staudinger-like reactions

Ye applied his catalytic system to enantioselective p-lactam and p-lactone formations via Staudinger-like reactions with imines or ketones (Scheme 14.22). Furthermore, the reaction with benzoyldiazenes gave the corresponding oxadiazin-6-ones issue of a [4+2] cycloaddition reaction, instead of the reported [2+2] DMAP derivatives, as nucleophilic catalysts. The postulated formation of an azolium enolate upon reaction of the NHC with the ketene in these reactions was evidenced experimentally by the isolation and full characterization of such zwitterionic adducts in model reactions. ... 

V./V-Dialkylhydraz()nes as the imine component in the Staudinger-like [2+2] cycloaddition to benzyloxyketene have been reported [71, 72]. The reaction led to the desired (3-lactams in excellent yields (84—98%), moderate to good selectivities (3R,45 > 35,4/ ), and only traces of trans isomers (3/ , 4/ ) were detected in some cases. 

One or two phosphorus atoms of tetraphosphacubane 9 can be reacted with suitable electrophiles. Those may be transition metal fragments <1996PS(113)15> or cationic organic groups <1999PS281>. The same counts for aza-tetraphosphaquadricyclane 50, which yields a complex family 51 or Staudinger reaction products like 52, for example <2001ZNB951>. 

As in similar cycloadditions of ketenes and alkenes, the Staudinger reaction is likely to occur via dipolar intermediates 4 in a thermally allowed two-step process to give ds-3,4-disubstituted azetidin-2-ones 5 stereoselectively. 

Across other double bonds The reaction of phenyl thiocyanate with P N compounds was first investigated by Staudinger and Meyer in 1919 . The reaction proceeds across the C=S bond of the isothiocyanate to give fragmentation products. For example, from ethyliminotriphenylphosphorane 67 and ethyl isothiocyanate a good yield of diethylcar-bodiimide and triphenylphosphine sulfide is obtained. The reaction most likely proceeds via the four-membered ring intermediate 68 formed in a [2+2] cycloaddition reaction. 

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