Shapiro reaction regioselectivity

Reductive lithiation of the vinylsulfide 67 derived from a cyclic ketone provides a valuable alternative to the Shapiro reaction (section 8.1),84 and the sequence of events leading to 68 or 69 determines the regioselectivity. 

P. Quayle and co-workers utilized the Dotz benzannulation reaction for the synthesis of diterpenoid quinones." The authors developed a novel synthetic approach to 12-O-methyl royleanone using a simple vinyl chromium carbene complex along with a disubstituted oxygenated acetylene. The bicyclic hydrazone was converted to the corresponding vinyllithium derivative by the Shapiro reaction and then functionalized to give the desired crude Fischer chromium carbene complex. The benzannulation took place in refluxing THF with excellent regioselectivity, and the natural product was obtained in 37% overall yield from the hydrazone. 

Regioselectivity in the context of substituted alkenyl anion has also been addressed. It is known that the base-induced fragmentation of tosylhydrazones (Shapiro reaction) derived from a-substituted ketones leads predominantly to the "kinetic" (cf. ketone enolates)... 

In the saussurea lactone synthesis by Grieco (Scheme 31) [18], cleavage of the C(2)-C(3) link was carried out by ozonolysis of the C(2)-C(3) double bond in compound 247, obtained regioselectively from tetrahydrosantonin 3b by a Shapiro reaction, to give diol 51. Subsequent elimination of both hycftoxyl groups in several steps yielded saussurea lactone (56). An improvement of tWs procedure, described by our group [17], was based on the transformation of diol 51 into diselenide 52, which could then be transformed directly into saussurea lactone (56) (see Scheme 8). 

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