Catalytic reactions Shapiro reaction

As described previously, the Shapiro reaction requires stoichiometric amounts of base to generate the alkyllithium reagents. An efficient catalytic method of the Shapiro reaction, which showed excellent regio- and stereo-selectivity, has also been reported. Indeed, the combination of ketone phenyl aziridinylhydrazones 116 and a catalytic amount of hthium amides leads to the corresponding alkene 117 in good overall yield (equation... 

An elegant application of the catalytic Shapiro reaction has been found in the synthesis of the natural product 129 (equation 45), a component of the sex pheromone of the summer fruit tortrix moth (Adoxophyes orana). ... 

Hydrazones based upon l-amino-2-phenylaziridine 23 have also been described. Use of excess base leads to the usual Shapiro reaction 15 however, a unique feature of hydrazones like 24 is that they form alkenes in the presence of only catalytic amounts of LDA.16 For example,... 

As noted above, the classical Shapiro reaction requires the use of >2 equiv of base to effect the conversion of an arylsulfonylhydrazone to an alkene. However, in recent work Yamamoto has described a catalytic version of the Shapiro reaction that employs aziridinyl hydrazones and is effective with only 5-30 mol% of added base.21 As shown above, treatment of hydrazone 34 with 5 mol% of LDA affords a 93% isolated yield of 35 with >99 1 stereoselectivity. This reaction is believed to proceed via metalation of 34 with LDA to yield 36. This intermediate decomposes with loss of styrene and nitrogen to provide vinyllithium reagent 37, which is protonated by diisopropylamine, regenerating the LDA base. Unfortunately this method is not amenable to the capture of the intermediate vinyllithium species with electrophiles. 

Catalytic Shapiro reaction. Small amounts of LDA in ether successfully promote the decomposition of hydrazones derived from Af-amino-2-phenylaziridine. fZl-Alkenes are the major products. 

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