3,3-Sigmatropic bond migration

Double-bond isomerization can also take place in other ways. Nucleophilic allylic rearrangements were discussed in Chapter 10 (p. 421). Electrocyclic and sigmatropic rearrangements are treated at 18-27-18-35. Double-bond migrations have also been accomplished photochemically, and by means of metallic ion (most often complex ions containing Pt, Rh, or Ru) or metal carbonyl catalysts. In the latter case there are at least two possible mechanisms. One of these, which requires external hydrogen, is called the nwtal hydride addition-elimination mechanism ... 

With phenylhydrazine, a mixture of pyrazoles 587 and 3H-indoles 591 were formed via conjugate addition, C=C bond migration and cyclic animation of the nitrile group or [3,3]-sigmatropic rearrangement of 3-amino-3-alkenenitriles 585, respectively [268a],... 

For example, CdS can mediate a symmetry forbidden [1,3] sigmatropic shift of hydrogen, Eq. (43) In the absence of oxygen, these cyclic derivatives of diphenyl-cyclobutene underwent a reversible double bond migration. Since the reaction was... 

The inverted process, however, of transforming 1,6-diphosphahexa-1,5-diene b into 3,4-diphosphahexadiene or divinyl diphosphane proceeds under very mild conditions [Eq. (51)]. The diphosphide, prepared from succinylchloride and phenylbis(trimethylsilyl)phosphane between —70 and — 80°C, rearranges after silyl migration above 0°C, forming the spectroscopically detectable 1,6-diphosphahexadiene intermediate, and finally ending up with the divinyl diphosphane via a [3.3] sigmatropic bond shift (101). 

The 3,3 sigmatropic leairangement of 2-octenyl vinyl ether (39) afforded 3-pentyl-4-pentenal (40) in 79% yield. The terminal double bond was converted to the methyl ketone (41) in 90% yield. The keto aldehyde (41) was converted to S-pentyl-2-cyclopentenone (42). The double bond migration gave 2-pen-tyl-2-cyclopentenone (dihydronotjasmone), which was converted to methyl dihydiojasmonate (43 Scheme 1 l).t08409 similarly, dihyctojasmone was synthesized from 2-octenyl allyl ether. 

Reactions, which are seemingly 1,3-sigmatropic rearrangements, have been carried out with various substrates. Cyclopropyl vinyl alcohols have been converted to 3-cyclopropylprop-2-enyl derivatives by treatment with acetic acid, ° pyridinium chlorochromate, thionyl chloride,benzenethiol, and diethylaminosulfur trifluoride, e.g. reaction of 3 with thionyl chloride to give Double bond migration has also been mediated by treatment... 

Sigmatropic rearrangement Migration of a a bond from one end of a conjugated tt eleetron system to the other. The Claisen rearrangement is an example. 

A sigmatropic shift is defined as a reaction wherein a cr bond migrates over one or more ir systems. Numbers in brackets are used to define the movement of the cr bond. An [i,j] sigmatropic rearrangement is the migration of a o bond flanked by one or more it systems to a new location i-1 and j-1 atoms away. Like many concepts in this chapter, sigmatropic shifts are... 

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