Tetrahedron report number 562 Vinylogous Mannich reactions: selectivity and synthetic utility Scott K. Bur ² and Stephen F. Martin p Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, TX 78712, USA Received 29 September 2000 Contents 1. Introduction 3221 2. Acyclic iminium ions reacting with acyclic dienols 3222 2.1. N-Acyl and trialkyl iminium ions 3222 2.2. O-Silylated nitrones 3222 2.3. Imine±Lewis acid complexes 3223 3. Acyclic iminium ions reacting with cyclic dienols 3224 3.1. N-Acyl and trialkyl iminium ions 3224 3.2. Imine±Lewis acid complexes 3225 3.3. O-Silylated nitrones 3227 4. Cyclic iminium ions reacting with acyclic dienols 3229 4.1. Natural products synthesis 3229 4.2. Stereoelectronic and steric effects in additions to six-membered ring iminium ions 3230 5. Cyclic iminium ions reacting with cyclic dienols 3231 5.1. Silyloxyfurans reacting with N-acyliminium ions 3231 5.2. Silyloxyfurans reacting with O-silylated nitrones 3236 5.3. Silyloxypyrroles and thiophenes reacting with N-acyliminium ions 3236 6. Intramolecular vinylogous Mannich reactions 3237 6.1. Rugulovasines A and B 3237 6.2. Yohimbone 3237 6.3. Spirocyclic lactone formation 3238 7. Conclusions 3238 1. Introduction The Mannich reaction, which is typi®ed by the addition of enols to iminium salts Eq. 1)), has become one of the more important carbon±carbon bond forming reactions in organic synthesis. The resulting b-aminocarbonyl compounds, termed Mannich bases, are versatile synthons that can be converted into a variety of useful derivatives including Michael acceptors, amino alcohols, and further func- tionalized carbonyl compounds. 1 These aminoalkylation reactions have recently been reviewed. 2 1 The vinylog of the Mannich reaction, in which the addition of a dienol or equivalent) to an iminium ion to produce a d-aminocarbonyl compound Eq. 2)), has recently garnered the interest of a number of researchers. Not only is the d-aminocarbonyl structural array seen in a number of natural products, but also it is a useful and versatile func- tional unit in its own right. 2 There have been several reviews in which selected accounts Tetrahedron 57 2001) 3221±3242 Pergamon TETRAHEDRON 0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0040-402001)00035-7 Keywords: Mannich reactions; iminium salts; enol ethers; stereospeci®city. p Corresponding author. Tel.: 11-512-471-3815; fax: 11-512-471-4180; e-mail: sfmartin@mail.utexas.edu ² Present address: Department of Chemistry, Emory University, Atlanta, GA 30322, USA.