Allylic nitro 2,31-rearrangements

Allylic nitro compounds form rr-allylpalladium complexes by displacement of the nitro group and react with nucleophiles, and allylation with the tertiary nitro compound 202 takes place at the more substituted side without rearrangement to give 203[8,9,128]. 

Allylic nitro compounds are obtained by the reacdon of cyclic ketones with nitromethane in the presence of 1,2-diaminoethane fl mol% as catalyst. Because exa-cyclic nitroalkenes are rearranged to the fi)iifo-cyclic fi,Y-nitroalkenes, allylic nitro compounds are selecdvely produced fEq. 3.21. ... 

Allylic nitro compounds undergo [2.3]sigmatropic rearrangement to afford rearranged alcohols, as shown in Eq. 7.4346 and Eq. 7.44 47 Because the allylic nitro compounds used in these reactions are readily prepared either by the Henry reaction or the Michael addition, these reactions may be useful in organic synthesis. 

Thermolysis of allylic nitro compounds results in the formation of rearranged allyl alcohols the cyclohexene 416, for instance, affords a 4 1 mixture of the cyclohexanol derivatives 417 and 418. It is proposed that the process involves a [2,3] sigmatropic shift of a nitro group (equation 137)451. 

Substitution reactions of allylic nitro compounds often lead to rearranged products, as in palladium(0)-catalysed aminations and alkylations. Thus treatment of the nitro ester 419 with piperidine in the presence of tetrakis(triphenylphosphine)palladium yields a mixture of the unrearranged and rearranged amines 420 (R = piperidin-l-yl) and 421... 

The carbanion derived from dimethyl malonate reacts with the cyclic nitro compounds 422 of ring size 5, 6, 7, 8 and 12 to afford the corresponding esters 423. Acyclic allylic nitro compounds 424 (R = Me, CH2OAC or CC Et) are attacked by bulky nucleophiles, such as dimethyl malonate anion, mainly at the terminal primary carbon atom to give rearranged products 425, whereas smaller nucleophiles, e.g. the anion derived from methyl cyanoacetate, react at the tertiary carbon atom to yield 426409a 453 455. 

In contrast, reaction of allylic nitro compounds 4 with sodium benzenethiolate in HMPT leads to rearranged allylic sulfides 5.2... 

Scheme 18.69 Rearrangement of allylic nitro compounds via a f2.31 process.—...

The utility of this method also stems from the fact that the nitro group enables C—C bond formation prior to the rearrangement. Michael addition of the anion derived from 276 to methyl vinyl ketone led to allylic nitro compound 277, which rearranged to allylic alcohol 278 in hi yield and excellent diastereoselectivity. Meanwhile, a single diastereomer of the bicyclic framework 280 was available under thermodynamic control from nitro aldehyde 279 via reversible Henry reaction, and transposition of the allylic nitro stereocenter to allylic alcohol 281 resulted from the suprafacial nature of the ensuing [2,3]-rearrangement. 

Subsequently, these authors have also studied the effect of polar factors on the sulfenate-sulfoxide equilibrium and obtained similar results to those reported by Braverman and coworkers . For example, reaction of 2,4-dinitrobenzenesulfenyl chloride with lithium allyl-a-dj alcoholate gives only (or perhaps mainly ) allyl-a-d2 2,4-dinitrobenzenesulfenate, whereas the corresponding reaction with 4-nitrobenzenesul-fenyl chloride results in complete ( > 99%) rearrangement to the sulfoxide. However, when a single nitro group is located in the ortho position, the ratio (K) of sulfenate to sulfoxide approaches unity. This ratio is also affected by the polarity of the solvent and changes from 1.43 in CCI4 to 0.39 in chloroform, consistent with the results described above for the equilibrium shown in equation 9. 

The reaction of 2-chloroisobutyrophenones and nitromethanide anion has stereose-lectively provided ( )-3-nitro allylic alcohols.58 The Gibbs free enthalpies of reaction in DMSO for carbanion addition, epoxide formation, and rearrangement to 3-nitro allylic alcohol, as elementary steps for the reaction, have been estimated from corresponding neutral gas reactions and using a thermodynamic approach to the transfer of gaseous compounds to DMSO. 

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