Question

Show how to convert 1-bromopentane to each of these compounds using a lithium diorganocopper (Gilman) reagent. Write an equation, showing structural formulas, for each synthesis. (a) Nonane (b) 3-Methyloctane (c) 2,2-Dimethylheptane (d) 1-Heptene (e) 1-Octene

Short answer

Question: Convert 1-bromopentane to different compounds using a lithium diorganocopper (Gilman) reagent. Show the reactions to synthesize (a) nonane, (b) 3-methyloctane, (c) 2,2-dimethylheptane, (d) 1-heptene, and (e) 1-octene. Answer: To convert 1-bromopentane to the different compounds, perform the following reactions: (a) $$ C_5H_{11}Br \ + \ C_4H_7Li \ → \ C_9H_{20} \ + \ LiBr $$ (b) $$ C_5H_{11}Br \ + \ C_3H_5Li \ → \ C_8H_{18} \ + \ LiBr $$ (c) $$ C_5H_{11}Br \ + \ C_4H_5Li \ → \ C_9H_{20} \ + \ LiBr $$ (d) $$ C_5H_{11}Br \ + \ C_2H_2Li \ → \ C_7H_{14} \ + \ LiBr $$ (e) $$ C_5H_{11}Br \ + \ C_3H_4Li \ → \ C_8H_{16} \ + \ LiBr $$

Step-by-step solution

(a) Nonane

To synthesize nonane from 1-bromopentane, we would need a Gilman reagent that contains a four-carbon chain. First, create this reagent using 1-butyne and lithium (in excess) in diethyl ether. The equation for this step is: $$ C_4H_8 \ + \ 2Li \ \ → \ C_4H_7Li $$ Next, perform the reaction between 1-bromopentane and the Gilman reagent (lithium butylcuprate). The organic products combine to form nonane: $$ C_5H_{11}Br \ + \ C_4H_7Li \ → \ C_9H_{20} \ + \ LiBr $$

(b) 3-Methyloctane

To synthesize 3-methyloctane from 1-bromopentane, we would need a Gilman reagent that has a three-carbon chain with a methyl group branching off the second carbon. Create this reagent using 2-methyl-1-propyne and lithium (in excess) in diethyl ether. The equation for this step is: $$ C_4H_6 \ + \ 2Li \ → \ C_3H_5Li$$ After forming the Gilman reagent (lithium iso-butylcuprate), perform the reaction between 1-bromopentane and the Gilman reagent. The organic products combine to form 3-methyloctane: $$ C_5H_{11}Br \ + \ C_3H_5Li \ → \ C_8H_{18} \ + \ LiBr $$

(c) 2,2-Dimethylheptane

To synthesize 2,2-dimethylheptane from 1-bromopentane, we would need a Gilman reagent that has a two-carbon chain with two methyl groups branching off the second carbon. Create this reagent using 2,2-dimethyl-propyne and lithium (in excess) in diethyl ether. The equation for this step is: $$ C_5H_8 \ + \ 2Li \ → \ C_4H_5Li $$ After forming the Gilman reagent (lithium tert-butylcuprate), perform the reaction between 1-bromopentane and the Gilman reagent. The organic products combine to form 2,2-dimethylheptane: $$ C_5H_{11}Br \ + \ C_4H_5Li \ → \ C_9H_{20} \ + \ LiBr $$

(d) 1-Heptene

To synthesize 1-heptene from 1-bromopentane, we need a Gilman reagent with a two-carbon chain and a terminal alkyne. Create this reagent using 1-propyne and lithium (in excess) in diethyl ether. The equation for this step is: $$ C_3H_4 \ + \ 2Li \ → \ C_2H_2Li $$ Next, perform the reaction between 1-bromopentane and the Gilman reagent (lithium vinylcuprate). The organic products combine to form 1-heptene with a C-C double bond: $$ C_5H_{11}Br \ + \ C_2H_2Li \ → \ C_7H_{14} \ + \ LiBr $$

(e) 1-Octene

To synthesize 1-octene from 1-bromopentane, we need a Gilman reagent with a three-carbon chain and a terminal alkyne. Create this reagent using 1-butene and lithium (in excess) in diethyl ether. The equation for this step is: $$ C_4H_6 \ + \ 2Li \ → \ C_3H_4Li $$ Lastly, perform the reaction between 1-bromopentane and the Gilman reagent (lithium allylcuprate). The organic products combine to form 1-octene with a C-C double bond: $$ C_5H_{11}Br \ + \ C_3H_4Li \ → \ C_8H_{16} \ + \ LiBr $$