Question

Although diazomethane ( ${\mathbf{CH}}_{\mathbf{2}}{\mathbf{N}}_{\mathbf{2}}$) is often not a useful reagent for preparing cyclopropanes,other diazo compounds give good yields of more complex cyclopropanes. Draw a stepwisemechanism for the conversion of diazo compound A to B, an intermediate in the synthesis ofsirenin, the sperm attractant produced by the female gametes of the water mold Allomyces.

Short answer

Answer

Step-by-step solution

Diazo compounds

A diazo compound is an organic system containing an azo group, i.e., two linked nitrogen atoms(${\mathbf{N}}_{\mathbf{2}}$), at the terminal carbon position. The general formula of a diazo compound is ${\mathrm{R}}_2\mathrm{C}={\mathrm{N}}^{+}={\mathrm{N}}^{-}$.

The azo group brings about resonance in the structure to which it is attached, as shown below:

Canonical structure of diazo compounds

Mechanism of conversion from A to B

The reaction is driven by the elimination of nitrogen, which is shown below:

Mechanism for formation of B