L,3 Rearrangement

Photochemically, the [l,3]-rearrangement is allowed in the sterically easily accessible suprafacial-suprafacial mode. A few of the many examples known are shown in Equations 12.80-12.83. 

Aluminium and copper Lewis acids effect a regioselective [l,3]-rearrangement of allyl vinyl ethers in moderate to good yields (Scheme 30). The use of trisubstituted alkenes leads to depressed levels of Claisen products.53... 

These isomerizations almost certainly involve [l,2]-shifts of H atoms as well as of alkyl groups. One cannot exclude that [l,3]-rearrangements may also play a role. The reaction product, adamantane, is formed under thermodynamic control under these conditions. It is the so-called stabilomer (the most stable isomer) of all the hydrocarbons having the formula C1QH16. 

Thermolysis of A -nitroenamines 80a leads to a-nitroimines 81 by [l,3]-rearrangement, or while 80b is converted to the thermodynamically more stable nitroenamine isomer 82 (equation 16) ,... 

Figure 6.2. Severe conformational restrictions due to A1-3 strain are placed on the intermediates in the asymmetric [l,3]-rearrangement of allylic amines, (a) The starting material (as well as the nitrogen-coordinated rhodium complex) favors the antiperiplanar conformation, (b) The Ji-bonded metal hydride intermediate is restricted to the 5-trans conformation.

The regioselective synthesis of pyrroles via [3,3]- and [l,3]-sigmatropic rearrangements of 0-vinyl oximes formed by iridium-catalysed isomerization of 0-allyl oximes is such that when enolization is favoured, a [3,3]-rearrangement followed by a Paal-Knorr cyclization gives a 2,3,4-trisubstituted pyrrole and when enolization is disfavoured, a [l,3]-rearrangement occurs prior to enolization to give a 2,3,5-trisubstituted pyrrole after cyclization (Scheme 10). ... 

The synthesis of a-imino aldehydes through the thermal [l,3]-rearrangement of 0-alkenyl benzophenone oximes has been reported. A copper-mediated C-O bond coupling between benzophenone oxime and alkenyl boronic acids provides access to 0-alkenyl oximes and a Horner-Wadsworth-Emmons olefination applied to the a-imino aldehyde products gives y-imino-a, -unsaturated esters (Scheme 166). ... 

Allyl vinyl ethers (66) undergo [l,3]rearrangements to give cyclopentanones (67) when heated with Pd° catalysts,in vivid contrast to the uncatalysed thermal rearrangement of compounds such as (66), which results in the formation of cycloheptenones. The recently developed oxyanionic Cope rearrangement of cyclononatrienols has been used by Paquette and Crouse as the key step in a brief synthesis of ( )-multifidene (68)/ Highly substituted alkylcyclopentenes may be prepared by [3 + 2]cycloadditions between allyl cations and olefins/ ... 

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