Rearrangement stereospecificity

Both (cis- and trans-) isomers rearrange stereospecifically to the cis-rearranged cyclopropane product (i.e. 257), the processes being apparently controlled by the same cis-anion intermediate (i.e. 256)... 

The final, critical oxidative spirocyclization of the 2,3-disubstituted indole to the spiro oxindole was effected by treatment of 124 with tert-butyl hypochlorite in pyridine to provide the labile 125 [Fig. (34)]. The Pinacol-type rearrangement was conducted by treating compound 125 with p-toluenesulfonic acid in THF/water. It is assumed that the chlorination of 124 proceeds from the least hindered face of the indole, to give the a-chloroindolene 125. The hydration of the imine functionality must also occur from the same a-face that is syn to the relatively large chlorine atom furnishing the syn-chlorohydrin 126, that subsequently rearranges stereospecifically to the desired spiro oxindole 127. 

They have postulated that the solvolysis of 3-substituted cyclobutyl tosylates 12 (X = Alkyl, Ar, Cl, OEt, SiR 3) proceeds through the initial formation of bicyclobutonium ion in the rate determining step, which rearranges stereospecifically to the cyclopropyl-... 

Keywords camphene, rearrangement, stereospecific, waste-free, gas-solid reaction, isobornyl halide... 

Even alkene starting materials without a terminal substituent may rearrange stereospecifically, and 169 gives products 171 with 60-96% ee.122 The same transition state model 170 reliably predicts the sense of the chirality transfer. 

The stereospecific insertion of 2-monosubstituted alkenyl carbenoids was successfully employed in the preparation of 1-alkyl-1-zircono-dienes. The Z and E carbenoids of 1-chloro-l-lithio-l,3-butadiene (69 and 70, respectively) are generated in situ fromE- andZ-l,4-dichloro-2-butene [53] (Scheme 25). Inversion of configuration at the carbenoid carbon during the 1,2-metalate rearrangement stereospecifically yields terminal dienyl zirconocenes 71 and 72 [54] (Scheme 25). As the carbenoid-derived double bond is formed in 9 1=Z E for 69 and >20 1=E Z isomeric mixtures for 70, the metalated dienes 71 and 72 are expected to be formed with the same isomeric ratio. Carbon-carbon bond formation was achieved by palladium-catalyzed cross-coupling with allyl or vinyl halides to give the functionalized products with >95 5 stereopurity [55-57]. 

Alkoxy-2-vinylcyclopropanes rearrange stereospecifically to 2-cyclopentenols under very mild conditions. Thus, the lithium salt of 2-vinyl-1-cyclopropanol (204) undergoes the vinylcyclopropane-cyclopentene rearrangement at room temperature (equation 137). ... 

Ligands with P, As, Sb or S donor atoms do not exert any stereospecific labilizing effect on carbonyl ligands, so that mixtures of isomers are often obtained in their direct reactions with the hexacarbonyls. They do however readily displace ligands such as CH3CN or piperidine from their complexes without any rearrangement. Stereospecific synthesis of cis and fac isomers can therefore be carried out in two stages as follows ... 

The dienol derivative (247), when heated, rearranges stereospecifically by a 1,5-sigmatropic hydrogen shift to (248), from which the aldehyde is obtained on hydrolysis. ... 

Claisen rearrangement—Stereospecific introduction of angular substituents ... 

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