Cope rearrangement allenyl

DFT calculations on the allenyl Cope rearrangement of xyn-7-allenylnorbornene have given results which were not consistent either with experiment or with earlier... 

In the reaction of disubstituted alkynes, 1,3-migration of the acetate takes place to give allenyl esters that can be versatile substrates, especially for [3,3]-Cope rearrangements.333 1,5-Enynes have proved to be versatile substrates for the preparation of perfumery agents such as sabinol334 and sabina ketone.335 Transannular systems undergo similar reactions.336... 

In addition to a-allenic a-amino acids, the corresponding allenic derivatives of y-aminobutyric acid (GABA) have also been synthesized as potential inhibitors of the pyridoxal phosphate-dependent enzyme GABA-aminotransferase (Scheme 18.49) [131,138-142]. The synthesis of y-allenyl-GABA (152) and its methylated derivatives was accomplished through Crabbe reaction [131], aza-Cope rearrangement [138] and lactam allenylation [139], whereas the fluoroallene 153 was prepared by SN2 -reduc-tion of a propargylic chloride [141]. 

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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