Sulfones, allenyl hetero-Cope rearrangement

Blechert has developed an interesting synthesis of 2-subsdtuted indoles which involves the conjugate addition of V-phenylhydroxylamine salts (or A(-phenylnitrones) to electron-deficient allenes, followed by carbanion-accelerated hetero-Cope rearrangement of the Michael adduct. For example, addition of the hydroxylamine salt (46) to the allenyl sulfone (47) produces the anion (48), which undergoes rapid 3,3-sigmatropic reanangement to afford the P-keto sulfone (49). Cyclization to the indole proceeds smoothly upon exposure to formic acid (Scheme 3). 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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