Amines 2.3 -Wittig rearrangement

The aza-[2,3]-Wittig rearrangement of a vinylaziridine-derived quaternary azir-idinium ylide (i.e., [2,3]-Stevens rearrangement) has recently been reported (Scheme 2.53) [86], The aziridinium ylide 219, generated by the intramolecular reaction of a copper carbenoid tethered to a vinylaziridine, underwent a [2,3]-Ste-vens rearrangement to furnish the bicydic amine 220 with the indolizidine skeleton. 

Sigmatropic rearrangements of anions of (V-allyl amines have also been observed and are known as aza-Wittig rearrangements.291 The reaction requires anion stabilizing substituents and is favored by (V-benzyl and by silyl or sulfenyl substituents... 

It has been shown that the tri-n-butyltin group can control the diastereoselection of an aza-[2,3]-Wittig rearrangement, and the silicon-assisted aza-[2,3]-Wittig rearrangement of crotyl-type amines has been used to furnish each diastereoisomer of the... 

A tandem aza-Wittig/heterocumulene-mediated annulation route was developed for the efficient production of 6,7,8,9-tetrahydro-benzothieno[2,3-r/]-l,2,4-triazolo[l,5-a]pyrimidin-10(3F/)-ones <05S1601>, and an amine oxide rearrangement was key to the regioselective preparation of pyrrolo[2,3-J]pyrimidines <0581164>. Hexahydro-2-phenacylidene-pyrimidines gave -lactam fused 8-aroyl-2,3,4,5-tetrahydro-7-hydroxy-6//-pyrrolo[l,2-a]py-rimidine-6-ones when treated with (COCl), in the presence of NaH <05IJH87>, and methyl... 

The amine a-anions (38a-c) failed to rearrange under conditions employed for the analogous ethers. The corresponding ammonium salts, on the other hand, readily isomerize via the derived ylides (Stevens rearrangement) in a process analogous to the 1,2-Wittig rearrangement. ... 

Pyrrolidinyl amides undoubtedly form Z((9)-enolates, and the [2,3]-Wittig rearrangement of the -alkene (entry 5, [69] is highly selective. The Z-alkene was not tested, and propargylic amide enolates do not rearrange [70]. Entry 5 also shows the highest yield in the Table. As will be seen, amides of C2-symmetric amines can be excellent chiral auxiliaries in this process. 

The reaction of amine 21 with -BuLi preceeded with a diastereoselectivity ratio of 3 2 which, by analogy to the Houk calculated transition state structure for the oxy-[3,2]-Wittig rearrangement, can be attributed to a presumably small difference in the transition state energies leading to each diastereoisomer. ... 

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