Give reasons why Bomford Stevens & Shapiro reactions give different alkenes preferably. Justify your answers with examples.
Bamford-Stevens Reaction
Tosylhydrazones give alkenes upon treatment with strong bases. This reaction is performed in two steps, where the intermediate diazo compound may be isolated. Subsequent reaction with protic or aprotic solvents strongly influences the outcome of the reaction.
This reaction may be used to effect the overall transformation of a ketone to an alkene.
If an organolithium is used as the base, the reaction follows another mechanism without occurrence of carbenium ions and carbenes (see Shapiro Reaction).
The treatment of tosylhydrazones with alkyl lithium reagents is called the Shapiro reaction.
Shapiro Reaction,
Shapiro Reaction, is the base-induced reaction of tosylhydrazones to afford alkenes. This reaction is carried out with two equivalents of an organo-lithium compound.
The advantage of the Shapiro over Bamford-Stevens Reaction is, that the resulting dianion does not rearrange, which can occur with intermediate carbenes and carbenium ions. Also the Shapiro reaction does not lead to high stereoselectivity between the E-isomers/Z-isomers.
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