Q5(a). Dichloroacetyl chloride with Et₃N, then cyclopentadiene
Write the structure of the product(s) and the intermediate formed in the following reaction: Cl₂CH–COCl with 1) Et₃N, 2) cyclopentadiene, heat.
Answer in brief
Intermediate: dichloroketene; product: 7,7-dichlorobicyclo[3.2.0]hept-2-en-6-one (cis-fused).
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Topic notes: pericyclic reactions, with every Civil Services, IFoS and Geo-Scientist PYQ →
Coversdichloroketene[2+2] cycloadditionketenecyclopentadienecyclobutanoneπ2s + π2a
All parts of Question 5
- 5(a) Dichloroacetyl chloride with Et₃N, then cyclopentadiene10 marks
- 5(b) Starting material A and the intermediates10 marks
- 5(c) 290 nm or 450 nm for a reaction through T₁?10 marks
- 5(d) Rotational spectroscopy10 marks
- 5(e) NMR at two field strengths; mass spectrum of a ketone10 marks