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.

CONTENTS 5458 5.1. Boekelheide Rearrangement 5458 5.2. Rearrangement of Nitrones and Related Compounds 5461 6. Miscellaneous Pericyclic Reactions of N-Oxyenamines 5466 7. Conclusions 5469 Author Information 5469 Corresponding Author 5469 Notes 5469 Biographies 5470 Acknowledgments 5470 Abbreviations 5470 References 5470

CONTENTS 1. Introduction 5004 2. Synthesis of Six-Membered Cyclic Oxime Ethers 1 and 2 5005 2.1. [4 þ 2]-Cycloaddition Reactions 5005 2.2. Intramolecular Cyclization of γ-Functionalized Oximes 5009 2.3. Intramolecular Cyclization of Functionalized O-Substituted Hydroxylamines 5012 2.4. Synthesis of SCOE from N-O-Containing Heterocyclic Derivatives 5012 2.4.1. Synthesis of SCOE from Other 1,2-Oxazines 5012 2.4.2. Synthesis of SCOE from Isoxazolines and Five-Membered Cyclic Nitronates 5014 2.5. Other Methods 5014 3. Chemical Properties of SCOE 5016 3.1. Reduction of SCOE 5016 3.1.1. Reduction of SCOE to Tetrahydro-2H-1,2oxazines 5018 3.1.2. Reduction of SCOE with 1,2-Oxazine Ring-Opening 5020 3.1.2.1. Reduction of SCOE to 1,4-Amino Alcohols. 5020 3.1.2.2. Reduction of SCOE to Carbonyl Compounds. 5021 3.1.2.3. Reduction of SCOE to γ-Hydroxyoximes. 5022 3.1.3. Reduction Reactions of SCOE with 1,2-Oxazine Ring Contraction 5022 3.1.3.1. Reduction of SCOE to Pyrrolidines. 5022 3.1.3.2. Reduction of SCOE to N-Hydroxypyrrolidines. 5023 3.1.3.3. Reduction of SCOE to Pyrroles. 5024 3.1.3.4. Reduction of SCOE to Aziridines. 5025 3.1.3.5. Reduction of SCOE to Furan Derivatives. 5025 3.2. Addition Reactions to the CdN Double Bond of SCOE 5026 3.3. 1,2-Oxazine Ring-Opening in SCOE 5027 3.4. Deoximation of SCOE 5028 3.5. 1,2-Oxazine Ring Rearrangements in SCOE 5028 3.6. 1,2-Oxazine Ring Fragmentation Reactions in SCOE 5030 4. SCOE in the Synthesis of Natural Products and Biologically Active Compounds 5031 4.1. Synthesis of Amino Acids 5032 4.2. Synthesis of Polyhydroxylated Pyrrolidines 5033 4.3. Synthesis of Pyrrolizidine and Indolizidine Alkaloids and Their Analogs 5033 4.4. Synthesis of Biologically Active 2-Aryl-Substituted Pyrrolidines and Amines 5035 4.5. Synthesis of Other Natural Compounds 5036 5. Conclusion 5037 Author Information 5037 Biographies 5038 Acknowledgment 5038 References 5038