Carbon−Carbon Bond Forming Reactions Mediated by Silicon Lewis Acids

Abstract

I. Introduction 733 II. Silicon Lewis Acids: Synthesis, Storage, and Solvent Compatibility 734 III. Lewis Acidity of Silicon Derivatives 735 IV. Principles of Action of SLA 737 V. Reactions of Acetals with Nucleophiles 737 A. Reactions with Enol Ethers 738 B. Reactions with Allylic Reagents 740 C. Reactions with Other Nucleophiles 742 VI. Reactions of Acetal-Like Compounds with Nucleophiles 743 VII. Reactions of Carbonyl Compounds with Nucleophiles 747 A. Reactions with π-Nucleophiles 747 B. Reactions with σ-Nucleophiles 751 C. Activation of Carbonyl Compounds by Combinations of Lewis Acids 752 VIII. Three-Component Coupling of a Carbonyl Compound, an Alkoxysilane, and a Nucleophile 753 IX. Activation of the CdN Bond 755 A. Reactions of Unfunctionalized Imines 755 B. Addition to Imines Containing Electron-Withdrawing Groups 755 C. Addition to Nitrones 757 D. Addition to Nitronates 758 X. Cycloaddition Reactions 759 A. Reactions of Acetals of R,β-Unsaturated Carbonyl Compounds 759 B. Activation of R,β-Unsaturated Carbonyl Compounds 760 C. Cycloaddition of Heterodienes and Heterodienophiles 762 XI. Conjugate Addition 763 A. Reactions of Organocopper Compounds 763 B. Other Conjugate Addition Reactions 764 XII. Miscellaneous Reactions 766 XIII. Acknowledgment 768 XIV. References 768 § This paper is dedicated to Professor Herbert Mayr on the occasion of his 55th birthday.

A Stable Structurally Characterized Phosphorus‐Bound Isocyanide and Its Thermal and Catalyzed Isomerization to the Corresponding Cyanide

“…Useful speculation on a reasonable pathway from 1 c and 1 d to 1 e and 1 f, respectively, is somewhat complicated by the assertion that Me 3 SiCN exists in equilibrium with its more reactive isocyanide isomer. [11] However, the formation of Me 3 SiNC is rather slow in solution (albeit in 1-chloronaphthalene rather than MeCN), thus taking approximately 10 minutes at 225 8C to reach an approximate concentration of 0.15 % relative to that of the cyano isomer. [12] It is therefore reasonable to conclude that this equilibrium would be reached even more slowly at room temperature, thus suggesting that the provenance of the isocyano isomers 1 e and 1 f and, through their isomerization, the cyano isomers 1 g and 1 h, respectively, is Me 3 SiCN and not Me 3 SiNC because of the almost instantaneous formation of 1 e and 1 f at room temperature.…”

“…The trend Me 3 SiOTf > Me 3 SiBr > Me 3 SiCl in Table 1 parallels their decreasing Lewis acidity. [11] Interestingly, when the isomerization of 1 f promoted by Me 3 SiCl was followed by 31 P NMR spectroscopic analysis, a transient signal at d = À1.7 ppm corresponding to 1 l, perhaps from an intermediate in a competing pathway, was observed (Scheme 5). It was expected that the addition of one equivalent of a Lewis acid (e.g., AlCl 3 or Me 3 SiX) to the isomerization reaction of 1 f to 1 h would establish an equilibrium that involves the formation of the [AlCl 3 Br] À ion or the pentavalent silicate [Me 3 Si(X)-Br]…”

Synthesis of new functionalized mono‐ and diphosphonic acids with five‐membered aza‐heterocycles moieties

“…It is shown that this reaction proceeds only at the presence of effective catalyst-trimethylsilyl triflate [5,9] -under mild conditions to give phosphonates 1 and diphosphonates 2. The ratio of these compounds 1,2 depends on the structure of aza-heterocycles, so phosphonate 1c predominate for starting bulky N-formyl-3,5-dimetyl-1H-pyrazole.…”

Microwave‐Assisted Solvent‐Free Synthesis of Bis(dihydropyrimidinone)benzenes and Evaluation of their Cytotoxic Activity

“…The major drawback associated with this protocol is the low yields, particularly for substituted aromatic and aliphatic aldehydes (27,28). This has led to the development of multistep synthetic strategies (29)(30)(31)(32)(33)(34) 3 , clays, etc. However, many of these methods involve expensive reagents, long reaction times, and high stoichiometric amount of catalysts, and difficult to handle especially on a large scale.…”