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.

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 .

(e) Carbenes have great synthetic utility, especially in the synthesis of cyclopropanes from alkenes. Based on your answers to (a)–(d), show a mechanism for the cyclopropanation of cyclohexene.

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

Cyclopropanation using any of the reagents discussed here is stereospecific.

(a) What does this say about the mechanism?

Predict the product of the following reactions.

(b)

Predict the product of the following reactions.

(a)

Cyclopropanation using any of the reagents discussed here is stereospecific.

(b) Draw a reaction coordinate diagram for cyclopropanation.

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.

(h) Of the reactions studied here in Chapter 8, cyclopropanation is most similar to which?

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?