The synthesis of -substituted bromoalkanes and their conversion into Grignard reagents

Article abstract of DOI:10.1016/S0022-1139(00)80484-4

Reaction of the nitroxide (CF3)2NO(.) (1) with the bromoalkanes RBr (R = Me, Et and Prⁿ) (1:1 molar ratio) gives the compounds (CF3)2NOCH2Br (4a) (69percent), (CF3)2NOCHBrMe (4b) (93percent) + (CF3)2NOCHBrCH2ON(CF3)2 (6) (6percent) and (CF3)2NOCHBrEt (4c) (16percent) + (CF3)2NOCHMeCH2Br (7) (76percent) + (CF3)2NOCH2CHBrMe (8) (3percent), respectively, together with the hydroxylamine (CF3)2NOH (3).Treatment of the sodium salt (CF3)2NONa (2) with the dibromoalkanes Br(CH2)nBr (n = 2 and 3) (1:1 molar ratio) in diglyme affords mixtures of elimination and substitution products, i.e.H2C=CHBr + (CF3)2NOCH2CH2Br (9a) + (CF3)2NOCH2CH2ON(CF3)2 (10a) (ratio 21:39:7) and (CF3)2NOCH2CH=CH2 (12) + (CF3)2NO(CH2)3Br (9b) + (CF3)2NO(CH2)3ON(CF3)2 (10b) (ratio 22:43:9).The α-substituted compounds 4a and 4b do not form Grignard reagents in diethyl ether, those formed from the β-substituted compounds 7 and 9a undergo elimination to give propene and ethene respectively, while that produced from the γ-substituted compound 9b is stable at room temperature and reacts with the chlorosilane MeSiCl3 to afford the compound (CF3)2NO(CH2)3SiCl2Me (20) (53percent).