Shapiro reaction limitations

The Shapiro reaction occurs when a tosylhydrazone 86, easily prepared from a ketone and tosylhydrazine, is treated with 2 equivalents of an ethereal solution of n-butyllithium 87, resulting first in the removal of the N—H proton to give the anion 88 and then of a one proton from the less-substituted a position to give the dianion 89. Elimination of lithium p-toluenesulfinate in the rate-limiting step gives the lithium aUtenyldiazenide 90, which suffers loss of nitrogen to afford the alkenyllithium 91 (equation 31) ° . ... 

The Shapiro reaction is important and useful but it is limited. We need to explore next a method with a wider scope - vinyl metals made from alkynes. The trick here is to add two things on the same side of the triple bond - typically one is a metal and the other a hydrogen atom or an organic fragment such as an alkyl group. 

The conditions originally employed for the Shapiro reaction involved treatment of the sulfonylhydrazone derivative with an alkyllithium reagent in hexane or ether solvent. Although these conditions are quite effective for the conversion of sulfonylhydrazones to alkenes (e.g., 1—>2), efforts to capture the intermediate vinyllithium reagent with electrophiles other than H+ are often met with limited success due to competing deprotonation of the solvent or the sulfonyl aryl group by the basic vinyllithium species. For example, treatment of 15a with >2 equiv of n-BuLi in hexane followed by quenching with D2O provided 16 in quantitative yield but with only -10% deuterium incorporation. A solution to this problem was developed independently by Shapiro and Bond that employs TMEDA (tetramethylethylenediamine) as an additive for Shapiro reactions.7,10 As shown below, use of TMEDA (4.0 equiv) as a cosolvent led to the conversion of 15b to 16 in quantitative yield with 95% deuterium incorporation. 

Methylenetetrahydrofuran-2-ones e.g. 32) have been the subject of much synthetic activity in recent years. Barrett S" has shown that the Shapiro reaction may be used to prepare these useful compounds by a one-pot process. The well documented severe limitations of the Shapiro reaction have been partially overcome by structural modifications. The dianion (29) reacts with ketones forming a new dianion that was converted to the trianion (30), which on warming evolves nitrogen to give (31) and that, upon treatment with CO2 followed by... 

S. A. Rice My answer to Prof. Manz is that, as I indicated in my presentation, both the Brumer-Shapiro and the Tannor-Rice control schemes have been verified experimentally. To date, control of the branching ratio in a chemical reaction, or of any other process, by use of temporally and spectrally shaped laser fields has not been experimentally demonstrated. However, since all of the control schemes are based on the fundamental principles of quantum mechanics, it would be very strange (and disturbing) if they were not to be verified. This statement is not intended either to demean the experimental difficulties that must be overcome before any verification can be achieved or to imply that verification is unnecessary. Even though the principles of the several proposed control schemes are not in question, the implementation of the analysis of any particular case involves approximations, for example, the neglect of the influence of some states of the molecule on the reaction. Moreover, for lack of sufficient information, our understanding of the robustness of the proposed control schemes to the inevitable uncertainties introduced by, for example, fluctuations in the laser field, is very limited. Certainly, experimental verification of the various control schemes in a variety of cases will be very valuable. 

Another promising approach to controlling processes such as chemical reactions is presented by Brumer cind Shapiro [59], using the coherence of lasers by applying nanosecond lasers with close to transform-limited bandwidth. 

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