Total Synthesis of (+/-)-Fawcettimine

Article abstract of DOI:10.1021/jo00268a015

(+/-)-Fawcettimine (7) has been prepared in 13 steps from cyano enone 14 along the line: 14 <*> 16 <*> 17 <*> 19 <*> 22 <*> 23 <*> 24 <*> 25 <*> 35 <*> 42 <*> 43 <*> 45 <*> 54 <*> 7.The overall yield is 16.6percent, and no protecting groups are required in the synthesis.The tautomeric ring-chain equilibria of keto carbinolamines 7, 57, and 60 and diketo amines 56 and 59 have been investigated by NMR spectroscopy and molecular mechanics calculations.In the 4R ("epi") series, diketo amine 56 seems to predominate over keto carbinolamine form 57.Isomer 60 cannot be observedspectrally, and the molecular mechanics calculations suggest that it should be 5 kJ/mol less stable than 57.These experiments and calculations are in agreement with the observation that compound 54 exists wholly in the keto amine form, with none of the carbinolamine tautomer being observable spectrally.In the 4S ("natural") series, the keto carbinolamine form 7 greatly predominantes over the diketo amine form 59.