| סיכום: | Heating a 2,5-furanocyclic (2-azidoethyl)allene initiates a cascade reaction comprising azide–allene cycloaddition, loss of nitrogen, and azatrimethylenemethane (ATMM) diyl–furan transannular (4+3)-cycloaddition. The major product of this reaction contains the pentacyclic core common to guanacastepenes D and H, and radianspenes J–L; in addition, the central oxabridged cycloheptene ring, flanked by two carbocyclic rings, is structurally related to the ABC-ring system found in the cortistatins. This is the first reported synthetic application of a ‘free’ (non-conjugated) ATMM. The cyclization precursors were prepared via the first reported examples of the Ireland–Claisen rearrangement of an ethynyl lactone.
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