A Novel Approach for Mannich-Type Bases Having a Terminal Olefin:  Zinc Triflate and Water-Promoted Cyclization/C−N Bond Cleavage Process

Mannich-Type Reaction of Aldimines with 2-Silyloxydienes Catalyzed by Ammonium Chloride

“…No cycloadduct was detected but a Mannich-type product and starting materials were observed. We suspect that the Mannich-type products are not formed via cyclization/ring-opening mechanism, as in the case of our previous reaction between N-benzyl-protected imine and 2-silyloxybutadiene using zinc triflate and water (Scheme 1) [19]. Additionally, further HCl work-up of the acyclic product 3a gave no cycloadducts but the β'-amino-α,β-enone was recovered.…”

“…Additionally, further HCl work-up of the acyclic product 3a gave no cycloadducts but the β'-amino-α,β-enone was recovered. However, N-benzyl-protected acyclic products afforded piperidones upon reaction with HCl [19], indicating that the acyclic product 3a is stable under acidic conditions.…”

“…However, Mannich-type reaction of imines with 2-silyloxydienes, which provides easy access to β-aminoketones having a terminal olefin, is still challenging because [4 + 2] type cycloadducts [7]- [15] or mixtures of Mannich-type products and cycloadducts [16] [17] [18] are obtained in most cases, as shown in Figure 1. Previously we first reported a highly effective Mannich-type reaction of imine with 2-silyloxydiene in the presence of zinc triflate and water [19] [20] [21] [22], which gave the corresponding β'-amino-α,β-enones as attractive skeletons for pharmaceutically useful compounds [23] [24] [25] [26]. Although many vinylogous Mannich-type reactions have been developed [27]- [36], only a few examples that describe the selective preparation of β'-amino-α,β-enones by the reaction of imine with 2-silyloxybutadiene have been reported so far.…”

Efficient synthesis of β’-amino-α,β-unsaturated ketones

“…This versatile synthon has been extensively used in the construction of β-amino acids [2], β-amino alcohols [3], and homoallylic amines [4–5], and can serve as building blocks for the preparation of nitrogen-containing molecules often found in medicinal chemistry [6–10]. Thus, the development of efficient and stereoselective reactions for a useful approach to chiral β-amino ketones is still of importance.…”

Zn(OTf)2-catalyzed three component, one-pot cyclocondensation reaction of some new octahydroquinazolinone derivatives and access their bio-potential

“…Consequently, there is scope for further improvement toward milder reaction conditions and better yields. In recent years, zinc triflate is a unique Lewis acid that is currently of great research interest (Ishimaru and Kojima, 2000). Octahydroquinazolinone derivatives have attracted considerable attention since they exhibit potent antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa (Kidwai et al, 2005) and calcium antagonist activity (Yarim et al, 2003).…”