10. Addition Reactions

Show what products you would expect from the following metathesis reactions, using the Schrock or Grubbs catalysts.

(b)

Which electrophilic addition reactions

d. form a five-membered ring intermediate?

What characteristics must the reactant of a stereospecific reaction have?

What reagents should be used to carry out the following syntheses?

In Section 10.8.1, you learned that alkenes react more quickly with electrophiles than do the corresponding alkynes (k_alkene/k_alkyne > 1). Explain why there is a greater disparity in the alkene versus alkyne reactivity in the addition of HBr as compared to the addition of Br₂ [The rate data are not real, but are meant to illustrate a real trend.]

What is the major product of the reaction of 1 mol of propyne with each of the following reagents?

d. Br₂ (2 mol)/CH₂Cl₂

Answer Problem 39 , parts a–h, using 2-butyne as the starting material instead of propyne.

c. Br₂ (1 mol)/CH₂Cl₂

The synthesis of five-membered lactones (cyclic esters) has been accomplished using the electrophilic addition of I―Cl to an alkyne. Suggest a mechanism for this cyclization reaction. (Structure modification of Yao, T.; Larock, R.C. J. Org. Chem. 2005, 70, 1432–1437.)

Drawing on what you know about the stereochemistry of alkene addition reactions,

a. write the mechanism for the reaction of 2-butyne with one equivalent of Br₂.

Which electrophilic addition reactions

a. form a carbocation intermediate? intermediate?

In the addition of just 1 mole of bromine to 1 mole of hex-1-yne, should the hex-1-yne be added to a bromine solution or should the bromine be added to the hex-1-yne? Explain your answer.

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (viii) Cl₂ (1 equiv.). If you expect two products, show both.

(c)

Protonation of which of the following alkenes would be faster?

Show what reagents would be needed to synthesize the pheromone of the omnivorous leafroller (OLR) using olefin metathesis to assemble the molecule at the double bond.