Sodium cyanoborohydride-hexamethylphosphoramide

B. Reduction of 1-Dodecyl Tosylate to n-Dodecane. In a dry 200-ml. three-necked flask equipped exactly as described in Section A are placed 50 ml. of hexamethylphosphoramide (HMPA), 1-dodecyl tosylate (6.80 g., 0.0201 mole) (Note 8), and sodium cyanoborohydride (5.02 g., 0.080 mole) (Note 3). The solution is stirred at 80° for 12 hours (Note 9), then diluted with 50 ml. of water, and extracted with three 60-ml. portions of hexane. The hexane solution is washed twice with water, dried over anhydrous magnesium sulfate, and then concentrated at reduced pressure with a rotary evaporator. Distillation of the residue through a short-path apparatus (Note 5) (Cautionl foaming) affords 2.49-2.64 g. (73-78%) of w-dodecane, b.p. 79-81° (3.75 mm.) na4D 1.4217 (lit.,3 n20d 1.4219) (Note 7). 

These preparations that illustrate the use of sodium cyanoborohydride in hexamethylphosphoramide as an effective, selective, and convenient procedure for the reduction of alkyl halides and tosylates is essentially the same as previously described.8 The very mild reducing ability of sodium cyanoborohydride makes the method particularly valuable when other functional groups are present in the molecule... 

Sodium cyanoborohydride in hexamethylphosphoramide selectively reduces alkyl iodides, bromides, and toluene-/ -sulphonates to the corresponding hydrocarbons aldehydes, ketones, etc., are not attacked. This allows the direct conversion of an alcohol into the corresponding hydrocarbon (Scheme 125) by hydride attack on the intermediate phosphite salt (197). 

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