Journal
TETRAHEDRON
Volume 67, Issue 6, Pages 1053-1061Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2010.12.051
Keywords
Phosphines; Allenoates; Chromans; 1,3-Dienes; [4+2] Annulation; Wittig olefination
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Funding
- National Natural Science Foundation of China [20872063]
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As an extension of our previous studies, the phosphine-mediated diverse reactivity of gamma-substituted allenoates with aldehydes has been further investigated. Under the catalysis of tris(p-chlorophenyl) phosphine (20 mol %), ethyl 2,3-pentadienoate, namely ethyl gamma-methyl allenoate, readily undergoes a formal [4+2] annulation with dual-functional salicylaldehydes, giving highly functionalized chromans in 47-97% yields. This transformation represents a novel reactivity pattern of electron-deficient allenes with aldehydes. Conversely, when the gamma substituent in the allenoate changes from methyl to benzyl or the employed phosphine from weakly nucleophilic triarylphosphine to strongly trialkylphosphine, the phosphine-mediated reactivity of gamma-substituted allenoates with aldehydes will be steered to a stoichiometric olefination reaction, leading to the highly stereoselective formation of (E,E)-1,3-dienes. Thus, under the mediation of equivalent PPh(3), ethyl gamma-benzyl allenoate readily condenses with salicylaldehydes, affording (E,E)-1,3-dienes in 34-84% yields; with strongly nucleophilic 1,3,5-triaza-7-phosphaadamantane (PTA) used instead of PPh3, ethyl gamma-methyl allenoate also gives the corresponding olefination products in 32-73% yields with reactive aromatic aldehydes. On the basis of our previous studies and current work, these chemical transformations of gamma-substituted allenoates with aldehydes, as well as their diverse reactivity, have been mechanistically rationalized. (C) 2010 Elsevier Ltd. All rights reserved.
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