[20757-87-3] · C5H7ClO · 5-Chloro-1-penten-3-one · (MW 118.56)
(reagent for the construction of fused ring systems and polyketones with 1,4- and 1,5-carbonyl relationships)
Physical Data: bp 25 °C/0.08 mmHg.
Solubility: sol most organic solvents.
Analysis of Reagent Purity: 1H NMR data are available.1
Preparative Method: not commercially available; prepared in a two-step sequence from b-chloropropionyl chloride and ethylene to give 1,5-dichloro-3-pentanone in 95% yield,2 which is then monodehydrochlorinated in 83% yield;3 earlier preparations4,5,6 of 1,5-dichloro-3-pentanone gave much lower yields.
Handling, Storage, and Precautions: use in a fume hood.
The reagent is used to generate a 2,6,10-triketone, which can be condensed to a tricyclic system1 by multiple intramolecular aldol condensations (eq 1). It is the synthetic equivalent of Divinyl Ketone; however, it allows sequential Michael addition of two different carbonyl compounds to produce an unsymmetrical 2,6,10-triketone, a procedure which is unsuccessful if used with divinyl ketone.
The reagent undergoes a Diels-Alder reaction to yield b-chloro ketones, which can be dehydrohalogenated to the vinyl ketones. Thiazolium salt catalyzed additions of aldehydes to the vinyl ketones lead to 1,4-diketones, which can be further elaborated by repeated sequences of the same type to 1,4,7-triketones and 1,4,7,10-tetraketones (eq 2).3
The Upjohn Company, Kalamazoo, MI, USA