Alkylation Synthetic Methods

The reaction of 2-aminothiazoles with alkyl isothiocyanates yields 2-thiazolylthioureas (30.3, 490), otherwise usually obtained by direct heterocyclization (Chapter II. Section II.4). Other synthetic methods... 

The most useful synthetic method involves the reaction of A-4-thiazoline-2-thione with the appropriate alkylating agent (see Section I.l.C). An example is given Scheme 54. 

The physical properties of the principal alkyl- and arylselenazoles synthesized are given in Table X-1 along with the synthetic methods used and bibliographic references. 

Alkylation of benzene with alkyl halides m the presence of aluminum chloride was discovered by Charles Friedel and James M Crafts m 1877 Crafts who later became president of the Massachusetts Institute of Technology collaborated with Friedel at the Sorbonne m Pans and together they developed what we now call the Friedel-Crafts reaction into one of the most useful synthetic methods m organic chemistry... 

With a regioselectivity opposite to that of the Zaitsev rule the Hofmann ehmma tion IS sometimes used in synthesis to prepare alkenes not accessible by dehydrohalo genation of alkyl halides This application decreased in importance once the Wittig reac tion (Section 17 12) became established as a synthetic method Similarly most of the analytical applications of Hofmann elimination have been replaced by spectroscopic methods... 

Acetoacetic ester synthesis (Section 21 6) A synthetic method for the preparation of ketones in which alkylation of the enolate of ethyl acetoacetate... 

The importance of quinones with unsaturated side chains in respiratory, photosynthetic, blood-clotting, and oxidative phosphorylation processes has stimulated much research in synthetic methods. The important alkyl- or polyisoprenyltin reagents, eg, (71) or (72), illustrate significant conversions of 2,3-dimethoxy-5-methyl-l,4-ben2oquinone [605-94-7] (73) to 75% (74) [727-81-1] and 94% (75) [4370-61-0] (71—73). 

Allyl Complexes. Allyl complexes of uranium are known and are usually stabilized by cyclopentadienyl ligands. AEyl complexes can be accessed via the interaction of a uranium halide and an allyl grignard reagent. This synthetic method was utilized to obtain a rare example of a "naked" homoleptic allyl complex, U(T -C2H )4 [12701 -96-17, which decomposes at 0°C. Other examples, which are more stable than the homoleptic allyl complex have been synthesized, ie, U(allyl)2(OR)2 (R = alkyl), U(allyl)2X (X = halide), and U(allyl)(bipy)2. 

Methyl ketones are important intermediates for the synthesis of methyl alkyl carbinols, annulation reagents, and cyclic compounds. A common synthetic method for the preparation of methyl ketones is the alkylation of acetone derivatives, but the method suffers limitations such as low yields and lack of regioselectivity. Preparation of methyl ketones from olefins and acetylenes using mercury compounds is a better method. For example, hydration of terminal acetylenes using HgSO gives methyl ketones cleanly. Oxymercuration of 1-olefins and subsequent oxidation with chromic oxide is... 

The procedure described is an example of a more general synthetic method for the direct conversion of ketones into cyanides. " The reaction has been carried out successfully with acyclic and cyclic aliphatic ketones, including numerous steroidal ketones and aryl-alkyl ketones. The conversion of diaryl or highly hindered ketones such as camphor and )3,j8-dimethyl-a-tetralone requires the use of a more polar solvent. The dimethoxyethane used in the present procedure should be replaced by dimethyl sulfoxide. ... 

Since Stork et al. introduced as a new synthetic method the alkylation and acylation of carbonyl compounds via enamines, this class of compounds has been the subjeet of intensive studies 1-3). The exceptional physical and chemical behavior of the enamine structure can be ascribed to resonance by conjugation of the unshared pair of electrons of the nitrogen atom with the 77 electrons of the double bond ... 

Because of the great range of structures containing cyclic hydroxamic acid functions it is difficult to give a concise summary of the available synthetic methods. Nevertheless, the vast majority of published syntheses depend on condensation reactions involving only familiar processes of acylation or alkylation of hydroxylamine derivatives. The principles of such syntheses are outlined in a number of typical examples in Section III, A but no attempt has been made to cover all reported cases. 

It is sometimes impossible to isolate the resultant jS-ketonitrile derivatives as such as they are unstable and readily polymerize, e.g. cyano-acetone. They are therefore identified as their corresponding arylhydrazones. The simpler alkyl-w-cyanomethyl ketones are, however, much more stable and their production through the cleavage of 5-alkylisoxazoles has been suggested as a preparative synthetic method. ... 

The reaction of potassium phthalimide 1 with an alkyl halide 2 leads to formation of a N-alkyl phthalimide 3/ which can be cleaved hydrolytically or by reaction with hydrazine (Ing-Manske variant) to yield a primary amine 5. This route owes its importance as a synthetic method to the fact that primary amines are prepared selectively, not contaminated with secondary or tertiary amines. 

Although interesting from a mechanistic point of view, alkane halogenation is a poor synthetic method for preparing alkyl halides because mixtures of products invariably result. For example, chlorination of methane does not stop cleanly at the monochlorinated stage but continues to give a mixture of dichloro, trichloro, and even tetrachloro products. 

The first series of soluble oligo(/ ara-phenylene)s OPVs 24 were generated by Kern and Wirth [48] and shortly after by Heitz and Ulrich [49]. They introduced alkyl substituents (methyls) in each repeat unit and synthesized oligomers 24 up to the hexamer. Various synthetic methods, like the copper-catalyzed Ullmann coupling, the copper-catalyzed condensation of lithium aryls, and the twofold addition of organomelallic species to cyclohexane-1,4-dione, have been thereby investigated. 

In a systematic study, it was demonstrated that, using a specially designed bulky benzamidinate ligand, it is possible to isolate mono(amidinato) dialkyl complexes over the full size range of the Group 3 and lanthanide metals, i.e., from scandium to lanthanum. The synthetic methods leading to the neutral and cationic bis(alkyls) are summarized in Scheme 56. Figure 18 displays the molecular structures of the cations obtained with Sc, Gd, and La. ... 

The syntheses and spectroscopic and electrochemical characterization of the rhodium and iridium porphyrin complexes (Por)IVI(R) and (Por)M(R)(L) have been summarized in three review articles.The classical syntheses involve Rh(Por)X with RLi or RMgBr, and [Rh(Por) with RX. In addition, reactions of the rhodium and iridium dimers have led to a wide variety of rhodium a-bonded complexes. For example, Rh(OEP)]2 reacts with benzyl bromide to give benzyl rhodium complexes, and with monosubstituted alkenes and alkynes to give a-alkyl and fT-vinyl products, respectively. More recent synthetic methods are summarized below. Although the development of iridium porphyrin chemistry has lagged behind that of rhodium, there have been few surprises and reactions of [IrfPorih and lr(Por)H parallel those of the rhodium congeners quite closely.Selected structural data for rr-bonded rhodium and iridium porphyrin complexes are collected in Table VI, and several examples are shown in Fig. 7. ... 

For general reviews of enolate alkylation, see D. Caine, in Carbon-Carbon Bond Formation, Vol. 1, R. L. Augustine, ed., Marcel Dekker, New York, 1979, Chap. 2 C. H. Heathcock, Modem Synthetic Methods, 6, 1 (1992). 

Cyclization of linear fragments is one of the successful synthetic methods of preparing alkyl- or aryl-substituted cyclophosphazenes. An excellent synthon of this type is the Bezman s salt... 

In general, tetrazolium salts are prepared by (a) oxidation of formazans and (b) alkylation of tetrazoles. Therefore, synthetic methods for formazans and tetrazoles are discussed first, followed by some direct and miscellaneous methods. 

Dioxabicyclo[2.2.1]heptane naturally assumed the role of the principal target molecule. It represented a considerable synthetic challenge, for not only is it a strained bicyclic molecule containing the weak and labile 0—0 bond, but it is also a di(secondary-alkyl) peroxide which is the most difficult type to make by classical procedures 12). New synthetic methods of exceptional mildness were clearly needed to solve this problem. In the course of the development of such techniques and from a desire to establish their scope, a variety of saturated bicyclic peroxides have been obtained in addition to 2,3-dioxabicyclo[2.2.1]heptane. The question of how substitution patterns and ring sizes affect the reactivity of bicyclic peroxides has further served to broaden interest in the subject. 

---