Arene-promoted lithiation of 1,n-dihaloalkanes (n = 2-6): a comparative study

Abstract

The reaction of 1,n-dichloroalkanes 3a (n = 2-6) with an excess of lithium powder and a catalytic amount of 4,4’-di-tert-butylbiphenyl (DTBB; 2.5 mol %) in the presence of different carbonyl compounds [ButCHO, PhCHO, Et2CO, (CH2)4CO, (CH2)5CO, (CH2)7CO, (-)-menthone], in THF at -78 ºC leads, after hydrolysis with water, to the expected 1,(n+2)-diols 4, yields being < 25% for n = 2, 3 and in the range of 45-79% for n = 4-6. When the same protocol is applied to 1,n-bromochloroalkanes 3b and 1,n-dibromoalkanes 3c (n = 2-6), diols 4 are obtained in general with lower yields.