| Popis: |
The total synthesis of the originally assigned structure of vannusal B (2) and its diastereomer (d-2) are described. Initial forays into these structures with model systems revealed the viability of a metathesis-based approach and a SmI2-mediated strategy for the key cyclization to forge the central region of the molecule, ring C. The former approach was abandoned in favor of the latter when more functionalized substrates failed to enter the cyclization process. The successful, devised convergent strategy based on the SmI2-mediated ring closure utilized vinyl iodide (−)-26 and aldehyde fragment (±)-86 as key building blocks, whose lithium-mediated coupling led to isomeric coupling products (+)-87 and (−)-88 (as shown in Scheme 17 in the article). Intermediate (−)-88 was converted, via (−)-89 and (−)-90/(+)-91, to vannusal B structure 2 (as shown in Scheme 18 in the article), whose spectroscopic data did not match those reported for the natural product. Similarly, intermediate (+)-25, obtained through coup... |
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