5-Hexenoyl chloride

Intramolecular cyclization of unsaturated acyl chlorides. Tributyltin hydride reduces acyl chlorides to aldehydes by a free-radical chain reaction involving an acyl radical (I, 1193). Cekovic10 now finds that treatment of acyl chlorides with a double bond in the S- or 6-position with tributyltin hydride (azobisisobutyronitrile initiation) gives cyclohexanone derivatives. Thus 5-hexenoyl chloride (1) is converted into cyclohexanone (2), and citronelloyl chloride (3) is converted into menthone (4). 

In this case each of the products 52 and 53 may be considered to result from Cy 6, from Cy 5, or from both. On the basis of simpler examples it appears that a high selectivity toward the (Cy 6) radical in the Cy6/Cy5 case is the rule. For instance, 5-hexenal with BP in cyclohexane at 80°C gives cyclohexanone (41% yield) resulting from the (Cy 6) radical, with no trace of 2-methylcyclopentanone which would arise from the (Cy 5) radical.A similar result has been observed by Cekovic, who generated the unsaturated acyl radical by tributylstannyl reduction of the corresponding acyl chloride in boiling benzene. In this way 5-hexenoyl chloride afforded cyclohexanone in 36% yield with no trace of Cy5 products. 

The reaction is generally carried out at -78 °C in ether solution, and yields are often excellent, l or example, manicone, a substance secreted by male ants to coordinate ant pairing and mating, has been synthesized by reaction of lithium diethylcopper with (E)-2p4-dimethyl-2-hexenoyl chloride. 

In each case, the methyl borne by the first cycle (arrowed in the previous and following schemes) is brought by the methylcyclopentane or cyclohexane. This has been checked for the condensation of 2-hexenoyl chloride and cyclohexane-d 12 in presence of acetyl chloride. In NMR spectra, the signals of the... 

The tritium labelled V.fischeri AHL 31 was prepared with a specific activity of 45-55 Ci/mmol by the tritiation of the corresponding unsaturated precursor, AT-(3-oxo-4-hexenoyl)-L-HSL 30 in the presence of a homogeneous Wilkinson s catalyst, tris(triphenylphosphine)rhodium[I] chloride (Scheme 13) [71]. 

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