73565-76-1Relevant academic research and scientific papers
Endo/exo stereoselectivity in Diels-Alder reactions of α,β-Dialkylated conjugated enals to cyclic 1,3-dienes: Intermediates in the synthesis of (-)-β-santalol and its analogs
Chapuis, Christian,Skuy, David,De Saint Laumer, Jean-Yves,Brauchli, Robert
, p. 1470 - 1516 (2015/02/19)
Highly exo-selective [4+2] cycloadditions of cyclopenta-1,3-diene 2a to α,β-dialkyl conjugated enals 5 are compared with the analogous endo-favored Diels-Alder reaction of cyclohexa-1,3-diene 7. The exostereoselectivity is lower in the homologous case of methylcyclopenta-1,3-diene 9. This diastereoselectivity is discussed either in terms of a retro-homo-Diels-Alder reaction, associated with thermodynamic control, or with respect to either a competing hetero-Diels-Alder/Claisen or Cope domino pathway, or retro-Claisen/retro-hetero-Diels-Alder of the endo-homo-cycloadducts. These hypothetical mechanisms have been examined by DFT calculations at the MPW1K(CH2Cl2)/6-31+G? ? level of theory for the AlCl3-mediated cycloadditions of 5d to 2a and 7. Application of Corey's methodology to the g-halogenoa- methyl-substituted dienophiles 5a and 5b allowed an enantioselective preparation of known and useful intermediates for the synthesis of either the naturally occurring (-)-β-santalol or its potentially olfactive structural analogs.
