A 50-ml., round-bottomed flask, equipped with a Teflon®-covered magnetic stirring bar and a reflux condenser connected to a gas-inlet tube, is charged with 970 mg. (2.51 mmoles) of cholest-4-en-3β-ol (Note 1) and 30 ml. of o-xylene (Note 2). The mixture is stirred to effect solution before 1.67 g. (0.0125 mole) of N,N-dimethylacetamide dimethyl acetal (Note 3) is added. The flask is flushed with argon, then heated (Note 4) at reflux under a positive pressure of argon with vigorous stirring for 65 hours. After cooling, the volatile materials are removed at reduced pressure (Note 5), and the yellow, oily residue (1.2 g.) is chromatographed on 60 g. of silica gel with diethyl ether (Note 6). Elution of the column with 200 ml. of ether gives a mixture of cholestadienes which is discarded; further elution with 500 ml. of ether affords 740 mg. of N,N-dimethyl-5β-cholest-3-ene-5-acetamide as a clear, colorless oil, which on trituration with acetone gives 740 mg. (65%) of the amide as white plates, m.p. 128–129.5°.