10. Addition Reactions

Predict the product of the following reactions.

(b)

The reaction of an alkene with diazomethane forms a cyclopropane ring. Propose a mechanism for the reaction. (Hint: It is a concerted reaction.)

Show how you would accomplish each of the following synthetic conversions.

(b)

In addition to radicals, anions, and cations, a fourth class of reactive intermediates is carbenes. A neutral species, the simplest carbene has a molecular formula of CH₂.

(f) Cyclopropanation of (E)- and (Z)-3-methylhex-3-ene gives two different products. Rationalize this outcome.

When it is strongly heated, ethyl diazoacetate decomposes to give nitrogen gas and a carbene. Draw a Lewis structure of the carbene.

Show how you would accomplish each of the following synthetic conversions.

(c)

Nitrogen-containing heterocycles form particularly stable carbenes and are commonly used as ligands in organometallic chemistry. (a) Why is the carbene shown particularly stable? [It may be helpful to draw the molecular orbital picture.]

Predict the carbenoid addition products of the following reactions.

(c)

Predict the carbenoid addition products of the following reactions.

(b)

Provide an arrow-pushing mechanism for the cyclopropanation of cyclohexene with methylene carbene. Rationalize the outcome.

To determine the stereochemistry of curacin A by synthesis, it would have been necessary to prepare all stereoisomers of the C₁₇―C₂₀ cyclopropane fragment. How would the reaction in Figure 16.30 be modified to produce the other stereoisomers shown here?

Predict the carbenoid addition products of the following reactions.

a. trans-hex-3-ene + CH₂I₂, Zn(Cu)

b. cis-hex-3-ene + CH₂I₂, Zn(Cu)

Two chemists at Dupont found that ICH₂ZnI is better than diazomethane at converting a C=C bond to a cylcopropane ring. Propose a mechanism for the reaction, now known as the Simmons–Smith reaction in their honor.

The following transformation is used as an early step in the synthesis of cilastatin, a drug used to counter antibiotic resistance. Identify a possible reagent for this step.