Allenic hydroxylamine derivative

Recently, the scope of gold-catalyzed intramolecular exo-selective hydroaminations was expanded to allenic hydrazines and hydroxylaminesJ The former substrates afforded pyrazolidines in the presence of DTBM-SEGPHOS-Au complex J, whereas [Au2 (R)-xylyl-BINAP (OPNB)2] gave the best results in the cyclization of hydroxylamine derivatives to isoxazolidines. Excellent chemical yields and enantioselectivities were obtained in most cases, and the method was also applied to the synthesis of chiral tetrahydrooxazines. 

Cyclization on to unsaturated C=N bonds has been reported by a number of workers to proceed in the unusual 6-endo fashion preferentially. Generation of the initial radical by addition of either a tin-centred or a sulfiir-centred radical to an alkyne or allene has been demonstrated. Thus cyclization of vinyl radicals (produced by the BusSnH-mediated addition to alkynes) on to imines proceeds in a 6-endo manner to give functionalized piperidines (Scheme 21). In a similar manner, allyl radicals (generated by Ts addition to allenes) add in a 6-endo manner to hydroxylamine derivatives. EUmination of the RO leads to the formation of dihydropyridines (Scheme 22). Functionalized bicyclic j8-lactams can be produced by an unusual 1-endo cyclization triggered by a similar addition of a tin-centred or sulfur-centred radical to substituted Af-propargyl )3-lactams. ... 

Addition of arylhydroxylamines to electrophilic allenes such as methyl propadienoate or l-methancsulfonyl-l,2-propadiene is another route to 0-vinyl derivatives[2]. The addition step is carried out by forming the salt of the hydroxylamine using NaH and the addition is catalysed with LiO CCFj. The intermediate adducts are cyclized by warming in formic acid. Yields are typically 80% or better. 

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