Lithium Aluminum Hydride Reduction of 1-Aryl-3-halopropenes, 1-Aryl-3-halobutenes, and (9-Anthryl)arylmethyl Halides. Nucleophilic Substitution vs. Single Electron Transfer

Article abstract of DOI:10.1021/jo00211a002

Lithium aluminum hydride reduction of ambident 1-aryl-3-halopropenes (1a-g), 1-aryl-3-halobutenes (4a-g), and (9-anthryl)arylmethyl halides (7a-i) was undertaken systematically.The reactivity of the halides and the regiochemistry of the reduction products were significantly influenced by various factors including the donor power of ethereal solvents, the substituent steric and electronic effects of the halides, the leaving groups, and the additive 12-crown-4.The reduction of 9- (α-bromo-3-chlorobenzyl)anthracene (7i) in tetrahydrofuran or diglyme afforded dimers 10-12 together with reduction products 8 and 9, with the ratio of alkylation products 8-9 vs. dimerization products 10-12 being around 2:1.When the reduction of 7i with lithium aluminium deuteride (LAD) was performed in the presence of 2 molar equiv of tributyltin hydride, however, a mixture of reduction products 8e and 9e was exclusively obtained, the d1 content being around 65 percent.In contrast, LAD reduction of 1-(3-chlorophenyl)-3-bromopropene (1g) and 1- (3-chlorophenyl)-3-bromobutene (4g) in the presence or absence of tributyltin hydride lead to the formation of only monodeuterated reduction products.On the basis of these results, the mechanism of reduction of these halides 1, 4, and 7 is discussed.