William P. Weber

Phase Transfer Catalysis in Organic Synthesis

1. Introduction and Principles.- 1.1 Introduction.- 1.2 Early Examples.- 1.3 The Coalescence of Ideas.- 1.4 The Principle of Phase Transfer Catalysis.- 1.5 Evidence for the Mechanism of Phase Transfer Catalysis.- 1.6 Charged Catalysts: Quaternary Ions.- 1.7 Uncharged Catalysts: The Amines.- 1.8 Uncharged Catalysts: The Crown Ethers.- 1.9 Uncharged Catalysts: The Cryptands.- 1.10 Catalyst Comparisons.- 1.11 Solvents.- 1.12 The Role of Water in Phase Transfer Catalysis.- 1.13 Summary.- References.- 2. The Reaction of Dichlorocarbene With Olefins.- 2.1 Introduction.- 2.2 The Mechanism of the Dichlorocyclopropanation Reaction.- 2.3 Catalytic Cyclopropanation.- 2.4 Dichlorocyclopropanation of Simple Olefins.- 2.5 Cyclopropanation of Enamines.- 2.6 Dichlorocyclopropanation Followed by Rearrangement.- 2.7 Carbene Addition to Indoles.- 2.8 Carbene Addition to Furans and Thiophenes.- 2.9 Carbene Addition to Polycyclic Aromatics.- 2.10 Carbene Addition to Conjugated Olefins.- 2.11 Michael Addition of the Trichloromethyl Anion.- 2.12 Dichlorocarbene Addition to Allylic Alcohols: A Cyclopentenone Synthon.- 2.13 Dichlorocarbene to Phenols: Reimer-Tiemann Reactions.- References.- 3. Reactions of Dichlorocarbene With Non-Olefinic Substrates.- 3.1 Introduction.- 3.2 C - H Insertion Reactions.- 3.3 Reaction With Alcohols: Synthesis of Chlorides.- 3.4 Carbene Addition to Imines.- 3.5 Addition to Primary Amines: Synthesis of Isonitriles...- 3.6 Reaction With Hydrazine, Secondary, and Tertiary Amines.- 3.7 Dehydration With Dichlorocarbene.- 3.8 Miscellaneous Reactions of Dichlorocarbene.- References.- 4. Dibromocarbene and Other Carbenes.- 4.1 Introduction.- 4.2 Dibromocarbene Addition to Simple Olefins.- 4.3 Dibromocarbene Addition to Strained Alkenes.- 4.4 Dibromocarbene Addition to Indoles.- 4.5 Dibromocarbene Addition to Michael Acceptors.- 4.6 Other Reactions of Dibromocarbene.- 4.7 Other Halocarbenes.- 4.8 Phenylthio- and Phenylthio(chloro)carbene.- 4.9 Unsaturated Carbenes.- References.- 5. Synthesis of Ethers.- 5.1 Introduction.- 5.2 Mixed Ethers: The Mechanism.- 5.3 Rate Enhancement in the Williamson Reaction.- 5.4 Methylation.- 5.5 Phenyl Ethers.- 5.6 Methoxymethyl Ethers of Phenol.- 5.7 Diethers From Dihalomethanes.- 5.8 The Koenigs-Knorr Reaction.- 5.9 Epoxides.- References.- 6. Synthesis of Esters.- 6.1 Introduction.- 6.2 Tertiary Amines and Quaternary Ammonium Salts.- 6.3 Noncatalytic Esterification in the Presence of Ammonium Salts.- 6.4 Polycarbonate Formation.- 6.5 Crown Catalyzed Esterification.- 6.6 Crown Catalyzed Phenacyl Ester Synthesis.- 6.7 Crown Catalyzed Esterification of BOC-Amino Acid to Chloromethylated Resins.- 6.8 Cryptate and Resin Catalyzed Esterifications.- 6.9 Synthesis of Sulfonate and Phosphate Esters by PTC.- References.- 7. Reactions of Cyanide Ion.- 7.1 Introduction.- 7.2 The Mechanism and General Features of the Cyanide Displacement Reaction.- 7.3 The Formation of Alkyl Cyanides.- 7.4 Formation of Acyl Nitriles.- 7.5 Synthesis of Cyanoformates.- 7.6 Cyanohydrin Formation.- 7.7 The Benzoin Condensation.- 7.8 Hydrocyanation, Cyanosilylation, and Other Reactions.- References.- 8. Reactions of Superoxide Ions.- 8.1 Introduction.- 8.2 Reactions at Saturated Carbon.- 8.3 Additions to Carbonyl Groups.- 8.4 Reactions With Aryl Halides.- References.- 9. Reactions of Other Nucleophiles.- 9.1 Introduction.- 9.2 Halide Ions.- 9.3 Azide Ions.- 9.4 Nucleophile Induced Elimination Reactions.- 9.5 Nitrite Ion.- 9.6 Hydrolysis Reactions.- 9.7 Anionic Polymerization Initiation.- 9.8 Organometallic Systems.- 9.9 Isotopic Exchange.- References.- 10. Alkylation Reactions.- 10.1 Introduction.- 10.2 The Substances Alkylated.- 10.3 Phase Transfer Alkylating Agents.- 10.4 Alkylation of Reisserts Compound.- References.- 11. Oxidation Reactions.- 11.1 Introduction.- 11.2 Permanganate Ion.- 11.3 Chromate Ion.- 11.4 Hypochlorite Ion.- 11.5 Catalytic Oxidation.- 11.6 Singlet Oxygen.- 11.7 Oxidation of Anions.- 11.8 Phosphorylation.- References.- 12. Reduction Techniques.- 12.1 Introduction.- 12.2 Borohydrides.- 12.3 Stoichiometric Reduction Systems.- 12.4 Other Catalytic Reductions.- 12.5 Altered Reactivity.- References.- 13. Preparation and Reactions of Sulfur Containing Substrates.- 13.1 Introduction.- 13.2 Preparation of Symmetrical Thioethers.- 13.3 Preparation of Mixed Sulfides.- 13.4 Preparation of Sulfides From Thiocyanates.- 13.5 Preparation of Alkylthiocyanates.- 13.6 Sulfides Resulting From Michael Additions.- 13.7 Synthesis of ?, ?-Unsaturated Sulfur Compounds.- 13.8 Other Phase Transfer Reactions of Sulfur Containing Substances.- References.- 14. Ylids.- 14.1 Introduction.- 14.2 Phase Transfer Wittig Reactions.- 14.3 The Wittig-Horner-Emmons Reaction.- 14.4 Sulfur Stabilized Ylids.- References.- 15. Altered Reactivity.- 15.1 Introduction.- 15.2 Cation Effects.- 15.3 Affected Anions.- 15.4 Ambident Nucleophiles.- References.- 16. Addendum: Recent Developments in Phase Transfer Catalysis.- Author Index.

Synthesis and photodegradation of poly [2,5-bis(dimethylsilyl) thiophene]

SummaryPoly[2,5-bis(dimethylsilyl)thiophene] (I), a copolymer with alternating thiophene and disilyl units, has been prepared by the Wurtz coupling of 2,5-bis(dimethylchlorosilyl)thiophene (IV) with sodium metal in toluene. I has been characterized by 1H, 13C, and 29Si NMR, IR, UV, GPC, TGA and elemental analysis. The photolysis of I in benzene/methanol solution results in degradation of the polymer. The structure of the photoproducts and possible mechanisms for their formation are discussed.

Photolysis of aryl-substituted disilanes in the presence of dimethyl sulfoxide

Abstract The photolysis of aryl-substituted disilanes in the presence of dimethyl sulfoxide has been studied. The products are found to be disiloxanes, aryl-substituted silanes, dimethylsilanone [(CH3)2Si=O], and dimethyl sulfide. Possible mechanisms for these reactions are discussed.

Synthesis and characterization of poly(1-methyl-1-silabutane), poly(1-phenyl-1-silabutane) and poly(1-silabutane)

SummaryAnionic ring opening polymerization of 1-methyl-1-silacyclobutane, 1-phenyl-1-silacyclobutane and 1-silacyclobutane co-catalyzed by n-butyllithium and hexamethylphosphoramide (HMPA) in THF at-78°C yields poly(1-methyl-1-silabutane), poly(1-phenyl-1-silabutane) and poly(1-silabutane) respectively. These saturated carbosilane polymers possess reactive Si-H bonds. They have been characterized by 1H, 13C and 29Si NMR as well as FT-IR and UV spectroscopy. Their molecular weight distributions have been determined by gel permeation chromatography (GPC), thermal stabilities by thermogravimetric analysis (TGA) and glass transition temperatures (Tg) by differential scanning calorimetry (DSC).

A convenient synthesis of 1,2-dimethyltetramethoxydisilane

Abstract Photolysis of methyldimethoxysilane in the gas phase yields 1,2-dimethyltetramethoxydisilane. The mass spectrum of 1,2-dimethyltetramethoxydisilane is discussed.

Synthesis of 3-methylene-1,1-dichlorosilacyclobutane and 1,1-dichlorosilacyclopent-3-ene

Abstract : Silacyclobutanes have played an important role in the development of modern silicon chemistry. For example, silacyclobutanes serve as precursors to carbon-silicon double bonded intermediates silenes as well as to pentacoordinate silicon anions in the gas phase. Silacyclobutanes also undergo facile ring opening polymerization. Despite the importance of this ring system surprisingly few functionalized silacyclobutanes and silacyclobutenes have been prepared. Similarly, there is considerable interest in 1-silacyclo-pent-3-enes due to their facile conversion into other functionalized silicon heterocycles as well as due to their ability to undergo anionic ring opening polymerization. These compounds have usually been prepared by reaction of a 1,3-diene with a dihalosilane under dissolving metal reduction conditions. (jes)

Insertion of dimethylsilylene into OH and NH single bonds

Abstract Dimethylsilylene, generated by photolysis of dodecamethylcyclohexasilane, inserts efficiently into OH single bonds of alcohols to yield alkoxydimethylsilanes. Use of ethanol-O- d 1 yields ethoxydimethylsilane-Si- d 1 . Dimethylsilylene also inserts into OH single bonds of water or D 2 O to yield respectively tetramethyldisiloxane or tetramethyldisiloxane-Si 2 - d 2 . Dimethylsilylene also inserts into NH bonds of primary and secondary amines to yield aminodimethylsilanes. This reaction provides an efficient route to difunctional silanes.

Synthesis of poly(silyl ethers) by Ru-catalyzed hydrosilylation

Abstract Dihydridocarbonyltris(triphenylphosphine)ruthenium, activated with a stoichiometric amount of styrene, catalyzes the hydrosilylation polymerization of dimethylsilyloxyaryl ketones or aldehydes as well as the copolymerization of aromatic α,ω-diketones and oligo-α,ω-dihydridodimethylsiloxanes to yield poly(silyl ethers). The ruthenium catalyzed addition of Si–H bonds across C–O double bonds to form CH–O–Si bonds is key to the polymerizations.

Synthesis and photodegradation of poly[2,5-bis(dimethylsilyl)furan]

SummaryPoly[2,5-bis(dimethylsilyl)furan] (V), a copolymer with alternating furan and disilyl units, has been prepared by the Wurtz coupling of 2,5-bis(dimethylchlorosilyl)furan (II) with sodium metal dispersion in toluene. Lower molecular weight poly[2,5-bis(dimethylsilyl)furan] (IV) has been prepared by a similar condensation reaction with 2,5-bis(dimethylfluorosilyl)furan (III). IV and V have been characterized by 1H, 13C and 29Si NMR, IR, and UV spectroscopy as well as by GPC, TGA and elemental analysis. Photolysis of V in a benzene/methanol solution results in degradation of the polymer.

Evidence for the intermediacy of 1,1-dimethyl-2-phenyl-1-sila-1,3-butadiene in the photochemistry and pyrolysis of 1,1-dimethyl-2-phenyl-1-sila-2-cyclobutene

Abstract Photolysis of 1,1-dimethyl-2-phenyl-1-sila-2-cyclobutene (I) in methanol and methanol-O- d 1 yields dimethylmethoxy(1-phenyl-2-propenyl)silane and dimethylmethoxy(1- d 1 -1-phenyl-2-propenyl)silane, respectively, as major products. These products may be formed by reaction of methanol or methanol-O- d 1 with 1,1-dimethyl-2-phenyl-1-sila-1,3-butadiene. Gas phase pyrolysis of I and acetone or formaldehyde have also been studied.