BackIn Section 10.8.1, you learned that alkenes react more quickly with electrophiles than do the corresponding alkynes (kalkene/kalkyne > 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.]
α-Pinene is a terpene found in pine trees. Starting from geranyl diphosphate (a terpene), draw the arrow-pushing mechanism to produce α-pinene. Assume that an enzyme active site will provide whatever acids and bases you might need.
Predict the products you would get when the following alkenes react under the following conditions: (i) H2SO4, H2O and (ii) 1. Hg(OAc)2, H2O , 2. NaBH4
(c)
Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (i) HBr; (ii) HCl; (iii) HBr, H2O2 (iv) H2SO4, H₂O (v) 1. Hg(OAc)2, H2O 2. NaBH4 ; (vi) 1. BH3 2. H2O2, NaOH
(d)
What stereoisomers are obtained when 2-butyne undergoes each of the following reaction sequences?
a. 1. H2/Lindlar catalyst 2. Br2/CH2Cl2
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.
Propose a mechanism for the triolefin process using a metal alkylidene as the catalyst.
Show what products you would expect from the following metathesis reactions, using the Schrock or Grubbs catalysts.
(b)
Protonation of which of the following alkenes would be faster?
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.)
Draw the mechanism for the following reaction:
When alkynes are treated with water and bromine a bromoketone is produced. Provide a plausible arrow-pushing mechanism that accounts for the formation of this product.
What reagents should be used to carry out the following syntheses?
What characteristics must the reactant of a stereospecific reaction have?
Which electrophilic addition reactions
a. form a carbocation intermediate? intermediate?