Practical Synthesis of 3b-Amino-5-cholestene and Related 3b-Halides Involving i-Steroid and Retro-i-Steroid Rearrangements.

[摘要]：Derivs. of 3b-amino-5-cholestene (3b-cholesterylamine) are of substantial interest as cellular probes and have potential medicinal applications. However, existing syntheses of 3b-amino-5-cholestene are of limited preparative utility. We report here a practical method for the stereoselective prepn. of 3b-amino-5-cholestene, 3b-chloro-5-cholestene, 3b-bromo-5-cholestene, and 3b-iodo-5-cholestene from inexpensive cholesterol. A sequential i-steroid/retro-i-steroid rearrangement promoted by boron trifluoride etherate and trimethylsilyl azide converted cholest-5-en-3b-ol methanesulfonate to 3b-azido-cholest-5-ene with retention of configuration in 93% yield.

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