The Allylic Rearrangement. II. Reactions of 5,5,5-Trichloro-3-penten-2-one with Nucleophiles

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Abstract
Reactions of 5,5,5-trichloro-3-penten-2-one (1) with a number of nucleophiles have been carried out. It was found that the Grignard reagents (5) primarily attacked the carbonyl carbon of 1 yielding the corresponding tertiary alcohols (7). The reaction sequence of ethylmagnesium bromide (5a) is given as an example. The reaction of 5a with 1 gave 6,6,6-trichloro-3-methyl-4-hexen-3-ol (7a) as the major constituent of the primary product. The hexenol 7a readily underwent the allylic rearrangement by heating at distilling temperature (88–90°C/6 mmHg) to afford 4,6,6-trichloro-3-methyl-5-hexen-3-ol (8a), which was in turn converted into 6,6-dichloro-3-methyl-3,4-epoxy-5-hexene (9a) by treatment with sodium methoxide. The stereoselective synthesis of dl-erythro-4,6,6-trichloro-3-methyl-5-hexen-3-ol (8a-I) was achieved by using 3,5,5-trichloro-4-penten-2-one (3) as the starting material in place of 1. dl-trans-6,6-Dichloro-3-methyl-3,4-epoxy-5-hexene (9a-I) was derived by the cyclization of 8a-I with a base. The stereochemistry of 8a and 9a was discussed on the basis of NMR data. Nucleophiles such as methanol, hydrogen chloride, anilines, thiophenol, sodium acetate, sodium phenolate, and diethyl sodiomalonate gave the products of the conjugate addition (15). Ethyl sodioacetoacetate gave 2-chloro-3-acetonyl-4-ethoxycarbonyl-5-methylfuran (17).