Synthesis 5 Alkenes

Alkene synthesis via alcohol dehydration is complicated by carbocation rearrangements A less stable carbocation can rearrange to a more sta ble one by an alkyl group migration or by a hydride shift opening the possibility for alkene formation from two different carbocations... 

ZSM-5 catalyst ZSM-5 zeolite Zudopenthixol [53772-Zvyagintsevite Zweifel alkene synthesis Zwikker reaction... 

COREY - WINTER Alkene synthesis Alkene synthesis from glycols via cyclic t, 2-lhionocartx)nates... 

The Julia alkene synthesis has been applied to allylsilane synthesis, including the synthesis of 2-cyclopentylidene- and 2-cyclobutylideneethyl(trimethyl)silanes30. 

The yields of the desulphonylation step are generally in the range of 70 to 80%. A related alkene synthesis is described in Section III.C.l. 

Three reaction sequences, all of a similar nature, have been published by Fujita and coworkers. The first175 is an alkene synthesis in which only three examples that involve sulphones are given. The most useful of these is a conversion of nerly phenyl sulphone (from neryl chloride) into aCn triene (75%), with the extra carbon atom being supplied by the iodomethylstannane reagent. The reaction proceeds spontaneously, with apparent retention of configuration at the Z alkene, as in equation (72). 

Arenesulphinylation 264 Arenesulphinylethanes, synthesis of 267 2-Arenesulphonyl-3-aryloxaziridines, as oxidizing agents 254 Arenesulphonyl azides, reactions of 641 At-Arenesulphonyliminopyridinium betaines, mass spectra of 160-162 Arenesulphonyl radicals 215, 1091 Aryldiazonium salts, reactions of 280, 281 Aryl(methylsulphinyl)(methylthio)alkenes, synthesis of 614... 

Two illustrations that show the power of this reaction for the preparation of strained cycloalkenes are the contractions of 102 to the propellane 103 , an application that has been reviewed , and of 104 to the bicyclo[2.1.1]hexene 105 . The utility of the Ramberg-Backlund rearrangement in the preparation of various natural products such as steroids , terpenoids and pheromones has been demonstrated. In addition to the synthetic applications mentioned in the previous subsection, several selected examples taken from the recent literature are given in equations 66-69. These examples further demonstrate the potential of this method for alkene synthesis in general. 

The reductive elimination of (3-hydroxysulfones is the final step in the Julia-Lythgoe alkene synthesis (see Section 2.4.3).301 The (3-hydroxysulfones are normally obtained by an aldol addition. 

Several methods for stereoselective alkene synthesis are based on boron intermediates. One approach involves alkenylboranes, which can be prepared from terminal alkynes. Procedures have been developed for the synthesis of both Z- and E-alkenes. 

The pros and cons of oxidative dehydrogenation for alkene synthesis using doped cerianites as solid oxygen carriers are studied. The hydrogen oxidation properties of a set of ten doped cerianite catalysts (Ce0.9X0.1Oy, where X = Bi, In, La, Mo, Pb, Sn, V, W, Y, and Zr) are examined under cyclic redox conditions. X-ray diffraction, X-ray photoelectron spectroscopy, adsorption measurements, and temperature programmed reduction are used to try and clarify structure-activity relationships and the different dopant effects. 

Stereoselective Alkene Synthesis via 1-Chloro-1-[(dimethyl)-phenylsilyl]-alkanes and a-(Dimethyl)phenylsilyl Ketones. 

Chiral active pharmaceutical ingredients, 18 725-726. See also Enantio- entries Chiral additives, 6 75—79 Chiral alcohols, synthesis of, 13 667-668 P-Chiral alcohols, synthesis of, 13 669 Chiral alkanes, synthesis of, 13 668-669 Chiral alkenes, synthesis of, 13 668—669 Chiral alkoxides, 26 929 Chiral alkynes, synthesis of, 13 668-669 Chiral ammonium ions, enantiomer recognition properties for, 16 790 Chiral ansa-metallocenes, 16 90 Chiral auxiliaries, in oxazolidinone formation, 17 738—739... 

Trisphenol epoxy novolacs, 10 371-372 Tristimulus colorimeters, 7 325 Trisubstituted alkene synthesis, 13 653 Trisubstituted silyl group, in silylation, 22 691... 

General.—The relatively unreactive diethyl arylmethylphosphonates have been used quite successfully in alkene synthesis with phase-transfer catalysis.100 In a comparative study it was shown that anions derived from /S-ketophosphonamides (109) have very low reactivity whereas those from 0-ketophosphonates (110) react quite well with aldehydes to give frwjj-alkenes.101 Benzyl dimethyl phosphonoacetate (111) can be used to form alkenes, e.g. (112), from which the benzyl group can be removed by hydrogenolysis without disturbing the C=C bond.102 The carbanions (113) can be... 

Among those phosphonates used successfully in alkene synthesis with aromatic aldehydes were (114),106 (115),107 (116),108(117),109 and(118).110 The stereochemical... 

Stereoselective Alkene Synthesis. Terminal alkynes can also be alkylated by organoboranes. Adducts are formed between a lithium acetylide and a trialkylborane. Reaction with iodine induces migration and results in the formation of the alkylated alkyne.24 25... 

From the data and accompanying analysis in a study of catalyzed chain growth polymerization of diethylzinc and n-alkene synthesis , we deduce that the reaction 2... 

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