Question

Show how to convert cyclopentene into these compounds. (a) trans-1,2-Dibromocyclopentane (b) cis-1,2-Cyclopentanediol (c) Cyclopentanol (d) Iodocyclopentane (e) Cyclopentane (f) Pentanedial

Short answer

Question: Describe the reaction steps required to convert cyclopentene into each of the following compounds: (a) trans-1,2-Dibromocyclopentane, (b) cis-1,2-Cyclopentanediol, (c) Cyclopentanol, (d) Iodocyclopentane, (e) Cyclopentane, and (f) Pentanedial. Answer: (a) To form trans-1,2-Dibromocyclopentane, cyclopentene must undergo bromination using Br2 in CCl4 at room temperature. (b) To form cis-1,2-Cyclopentanediol, cyclopentene must undergo syn dihydroxylation using OsO4/NMO. (c) To form Cyclopentanol, cyclopentene must undergo hydroboration with BH3/THF, followed by oxidation using H2O2/NaOH. (d) To form Iodocyclopentane, cyclopentene must undergo halogenation using I2 in HBr. (e) To form Cyclopentane, cyclopentene must undergo catalytic hydrogenation using H2 over Pd/C catalyst. (f) To form Pentanedial, cyclopentene must undergo ozonolysis using O3 followed by reduction with DMS or Zn/AcOH.

Step-by-step solution

Bromination of cyclopentene

To form trans-1,2-dibromocyclopentane, cyclopentene must undergo anti-addition of two bromine atoms across the double bond. This can be achieved using bromine (Br2) in the presence of an inert solvent like carbon tetrachloride (CCl4) at room temperature. The reaction proceeds as follows: Cyclopentene + Br2 (in CCl4) -> trans-1,2-Dibromocyclopentane (b) cis-1,2-Cyclopentanediol

Dihydroxylation

To form cis-1,2-cyclopentanediol, cyclopentene must undergo syn dihydroxylation, where two hydroxyl groups are added to the double bond, on the same side. This can be done using osmium tetroxide (OsO4) followed by the reduction with sodium bisulfite (NaHSO3) or using catalytic amount of OsO4 and a co-oxidant like N-methylmorpholine N-oxide (NMO). The reaction proceeds as follows: Cyclopentene + OsO4/NMO -> cis-1,2-Cyclopentanediol (c) Cyclopentanol

Hydroboration-oxidation

To form cyclopentanol, cyclopentene must undergo hydroboration followed by oxidation. This can be achieved using diborane (BH3) in tetrahydrofuran (THF) for the hydroboration step, followed by an oxidation using hydrogen peroxide (H2O2) in an aqueous alkaline solution. The reaction proceeds as follows: Cyclopentene + BH3/THF -> Cyclopentylborane + H2O2/NaOH -> Cyclopentanol (d) Iodocyclopentane

Halogenation

To form iodocyclopentane, cyclopentene must undergo an anti-addition of one iodine atom across the double bond. This can be achieved using iodine (I2) in the presence of HBr, which converts one I2 molecule into 2 HI molecules. The reaction proceeds as follows: Cyclopentene + I2 (in HBr) -> Iodocyclopentane (e) Cyclopentane

Catalytic hydrogenation

To form cyclopentane, the double bond in cyclopentene must be reduced. This can be done using hydrogen over a palladium on carbon (Pd/C) catalyst. The reaction proceeds as follows: Cyclopentene + H2 (in Pd/C) -> Cyclopentane (f) Pentanedial

Ozonolysis

To form pentanedial, cyclopentene must undergo ozonolysis, a process where the double bond is cleaved, and two carbonyl (C=O) groups are formed. This can be achieved using ozone (O3) in the presence of an inert solvent, followed by the reduction with dimethyl sulfide (DMS) or zinc/acetic acid. The reaction proceeds as follows: Cyclopentene + O3 (followed by DMS or Zn/AcOH) -> Pentanedial