[2207-27-4] · C7H6Cl4O2 · 5,5-Dimethoxy-1,2,3,4-tetrachlorocyclopentadiene · (MW 263.94)
Physical Data: yellow liquid with sweet odor; bp 108-110 °C/11 mmHg; d420 1.50 g cm-3.
Preparative Method: dechlorination of hexachlorocyclopentadiene in methanolic potassium hydroxide solution (eq 1).5
Purification: distillation under reduced pressure.
Handling, Storage, and Precautions: do not inhale the vapor; can cause dizziness. This reagent should only be used in a fume hood.
5,5-Dimethoxy-1,2,3,4-tetrachlorocyclopentadiene (1) is an excellent diene for Diels-Alder reactions. It undergoes cycloaddition reactions with Ethylene and subsequent reductive dechlorinations using Na/t-BuOH/THF to give 7,7-dimethoxynorbornene (eq 2).
A wide range of alkenes undergo [4 + 2] cycloaddition reactions with (1). The adducts can be used in the preparation of cyclopentane moieties. Reductive dechlorination of adducts followed by Potassium Permanganate oxidation yields cyclopentanone units (eq 3).
The bicyclic enone (2), which is useful for steroid synthesis, can be synthesized by Diels-Alder reaction with (1), followed by three subsequent steps. When (2) is treated with Vinylmagnesium Bromide followed by Potassium Hydride, (3) is obtained, which can be converted to steroids (eq 4).
The reaction of (1) with cyclic dienophiles can be used in the preparation of cis-fused bicyclo[4.n.0]dienes (eq 5).
Diels-Alder reactions of (1) with 3,3-dimethylcyclopropene followed by reductive dechlorination and acidic hydrolysis gives 7,7-dimethylcycloheptatriene (eq 6).
Norbornadienone can be synthesized from (1). Diels-Alder reaction of (1) with 1,2-dibromoethylene followed by a sequence of steps gives norbornadienone (eq 7).
Highly complex molecules like hexacyclo[184.108.40.206.2,7.0.4,9.010,14]tetradeca-5,12-diene can be synthesized by Diels-Alder reaction with (1) (eq 8).
James S. Panek, Nareshkumar F. Jain & Robert M. Garbaccio
Boston University, MA, USA