The reaction of vitamin D3 (I) with Ts-Cl in pyridine gives the tosylate (II), which is treated with NaHCO3 in hot methanol to yield 3,5-cyclovitamin D3 (III). The oxidation of (III) with SeO2 and tBu-OOH in dichloromethane, followed by acetylation affords 1-alpha-acetoxy-25-hydroxy-3,5-cyclovitamin D3 (IV). The dihydroxylation of the exo-double bond of (IV) with OsO4 in pyridine affords the alpha diol (V), which is oxidized with NaIO4 in methanol to provide the oxo cyclovitamin (VI). The reduction of (VI) with NaBH4 in ethanol gives the secondary alcohol (VII), which is mesylated with Ms-Cl and TEA in dichloromethane to yield the mesylate (VIII). The crude (VIII) is treated with LiAlH4 in THF to afford 1-alpha,25-dihydroxy-3,5-cyclovitamin D3 (IX). The cycloreversion of (IX) by means of hot acetic acid provides a mixture of the two monoacetylated vitamins (X) and (XI), which, without separation is hydrolyzed with KOH in methanol/ethyl ether to give the target 1-alpha,25-dihydroxy-19-nor-vitamin D3.

The 25-hydroxyvitamin D2 (I) is converted into the cyclovitamin D2 acetate (II) according to known methods. The dihydroxylation of the methylene group of (II) with OsO4 in pyridine gives vicinal diol (III), which is oxidized with NaIO4 yielding the ketonic cyclovitamin (IV). The reduction of the ketonic group of (IV) with NaBH4 in ethanol/water affords the corresponding hydroxy derivative (V), which is treated with mesyl chloride and triethylamine to give the mesylate (VI). The reduction of (VI) with LiAlH4 in THF yields the 19-nor-cyclovitamin D (VII), which is treated with hot acetic acid to afford both monoacetates (VIII) and (IX), separated by HPLC. Finally, both monoacetates (VIII) and (IX) are hydrolyzed with KOH in methanol.

The 25-hydroxyvitamin D2 (I) is converted into the cyclovitamin D2 acetate (II) according to known methods. The dihydroxylation of the methylene group of (II) with OsO4 in pyridine gives vicinal diol (III), which is oxidized with NaIO4 yielding the ketonic cyclovitamin (IV). The reduction of the ketonic group of (IV) with NaBH4 in ethanol/water affords the corresponding hydroxy derivative (V), which is treated with mesyl chloride and triethylamine to give the mesylate (VI). The reduction of (VI) with LiAlH4 in THF yields the 19-nor-cyclovitamin D (VII), which is treated with hot acetic acid to afford both monoacetates (VIII) and (IX), separated by HPLC. Finally, both monoacetates (VIII) and (IX) are hydrolyzed with KOH in methanol.

The methanolysis of vitamin D2 tosylate (XIV) gives the cyclovitamin (XV), which is oxidized with SeO2 and tert-butyl hydroperoxide in dichloromethane yielding the 1alpha-hydroxy cyclovitamin (XVI). The acylation of (XVI) with acetic anhydride affords the acetate (XVII), which is rearranged with TsOH in hot dioxane to provide 1alpha-acetodyvitamin D2 (XVIII). Finally, this com-pound is hydrolyzed with KOH in aqueous methanol.

The 25-hydroxyvitamin D2 (I) is converted into the cyclovitamin D2 acetate (II) according to known methods. The dihydroxylation of the methylene group of (II) with OsO4 in pyridine gives vicinal diol (III), which is oxidized with NaIO4 yielding the ketonic cyclovitamin (IV). The reduction of the ketonic group of (IV) with NaBH4 in ethanol/water affords the corresponding hydroxy derivative (V), which is treated with mesyl chloride and triethylamine to give the mesylate (VI). The reduction of (VI) with LiAlH4 in THF yields the 19-nor-cyclovitamin D (VII), which is treated with hot acetic acid to afford both monoacetates (VIII) and (IX), separated by HPLC. Finally, both monoacetates (VIII) and (IX) are hydrolyzed with KOH in methanol.

The 25-hydroxyvitamin D2 (I) is converted into the cyclovitamin D2 acetate (II) according to known methods. The dihydroxylation of the methylene group of (II) with OsO4 in pyridine gives vicinal diol (III), which is oxidized with NaIO4 yielding the ketonic cyclovitamin (IV). The reduction of the ketonic group of (IV) with NaBH4 in ethanol/water affords the corresponding hydroxy derivative (V), which is treated with mesyl chloride and triethylamine to give the mesylate (VI). The reduction of (VI) with LiAlH4 in THF yields the 19-nor-cyclovitamin D (VII), which is treated with hot acetic acid to afford both monoacetates (VIII) and (IX), separated by HPLC. Finally, both monoacetates (VIII) and (IX) are hydrolyzed with KOH in methanol.