Modular and stereoselective synthesis of hydroxylated angularly fused tricyclic piperidine derivatives via samarium diiodide mediated cyclization.

[摘要]：Proline-promoted Mannich reactions of a series of cycloalkanones with formalin and aniline followed by N-acetylation provided precursors I (n = 1-4) for SmI2-mediated cyclizations. The ketyl-aryl coupling of these compds. furnished angularly fused piperidine derivs. II (RR1 = bond, n = 1-4) in good yields. Highly stereoselective dihydroxylation gave the corresponding triols II (R = R1 = OH) with 5 contiguous stereogenic centers. Our modular approach to this type of compds. involves just 4 simple steps and is fairly general. For the conversion of I (n = 2) into II (RR1 = bond, n = 2) we could demonstrate that the toxic and carcinogenic additive HMPA can be successfully replaced by LiBr and 1,3-dimethyl-2-imidazolidinone (DMI).

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