Tert alkylation

In cases where Noyori s reagent (see p. 102f.) and other enantioselective reducing agents are not successful, (+)- or (—)-chlorodiisopinocampheylborane (Ipc BCl) may help. This reagent reduces prochiral aryl and tert-alkyl ketones with exceptionally high enantiomeric excesses (J. Chandrasekharan, 1985 H.C. Brown, 1986). The initially formed boron moiety is usually removed hy precipitation with diethanolamine. Ipc2BCl has, for example, been applied to synthesize polymer-supported chiral epoxides with 90% e.e. from Merrifield resins (T. Antonsson, 1989). 

In peptide syntheses, where partial racemization of the chiral a-carbon centers is a serious problem, the application of 1-hydroxy-1 H-benzotriazole ( HBT") and DCC has been very successful in increasing yields and decreasing racemization (W. Kdnig, 1970 G.C. Windridge, 1971 H.R. Bosshard, 1973), l-(Acyloxy)-lif-benzotriazoles or l-acyl-17f-benzo-triazole 3-oxides are formed as reactive intermediates. If carboxylic or phosphoric esters are to be formed from the acids and alcohols using DCC, 4-(pyrrolidin-l -yl)pyridine ( PPY A. Hassner, 1978 K.M. Patel, 1979) and HBT are efficient catalysts even with tert-alkyl, choles-teryl, aryl, and other unreactive alcohols as well as with highly bulky or labile acids. 

PEROXIDES AND PEROXIDE COMPOUNDS - ORGANIC PEROXIDES] (Vol 18) 4-alkoxy-5-tert-alkyl-2-sulfonamidophenol... 

In the presence of strong acid catalysts such as sulfuric acid, aUphatic (R CHO) aldehydes react with alkyl hydroperoxides, eg, tert-55ky hydroperoxides, to form hydroxyalkyl alkyl peroxides (1), where X = OH R, = hydrogen, alkyl and = tert — alkyl. 

In the presence of strong acid catalysts many commonly used commercial alkyl hydroperoxides decompose to acetone to some extent. Consequendy, the diperoxyketals derived from other ketones and alkyl hydroperoxides are often contaminated with small amounts of diperoxyketals derived from acetone (1, X = OOR, = methyl, R = R = tert — alkyl). 

A number of alternative multi-step procedures for the synthesis of a-tert-alkyl ketones are known, none of which possess wide generality. A previous synthesis of 2-tert-penty1cyclopentanone involved reaction of N-1-cyclopentenylpyrrol 1 dine with 3-chloro-3-methy1-l-butyne and reduction of the resulting acetylene (overall yield 46 ). However, all other enamines tested afford much lower yields. Cuprate addition to unsaturated ketones may be useful in certain cases. Other indirect methods have been briefly reviewed. ... 

Titanium(IV) is a powerful but selective Lewis acid which can promote the coupling of allylsilanes with carbonyl compounds and derivatives In the presence of titanium tetrachlonde, benzalacetone reacts with allyltnmethylsilane by 1,4-addition to give 4-PHENYL-6-HEPTEN-2-ONE. Similarly, the enol silyl ether of cyclopentanone is coupled with f-pentyl chloride using titanium tetrachlonde to give 2-(tert-PENTYL)CYCLOPENTANONE, an example of a-tert-alkylation of ketones. 

The reaction fails if the decarboxylation produces a radical that is easily oxidized, such as an a-hydroxyalkyl radical.2 In intermediate cases, such as tert-alkyl or a-alkoxyalkyl radicals,2 the yield based on the parent quinono is usually improved by using an excess of persulfate and carboxylic acid to compensate for the loss of radicals due to oxidation (footnote b, Table I). 

The reaction of tert-alkyl Grignard reagents with carboxylic acid chlorides in the presence of a copper catalyst provides ieri-alkyl ketones in substantially lower yields than those reported here.4,14 The simplicity and mildness of experimental conditions and isolation procedure, the diversity of substrate structural type, and the functional group selectivity of these mixed organocuprate reagents render them very useful for conversion of carboxylic acid chlorides to the corresponding secondary and tertiary alkyl ketones.15... 

Hexa(oligophenyl)benzenes (e. g. 31 or 33) present one possible approach to the realization of this aim. Two efficient synthetic routes have been elaborated for the preparation of hexa(terphenyl)- and hexa(quaterphenyl)benzene. The first, involving palladium-catalyzed trimerization of diarylacetylenes [54] as the key step, was demonstrated by the synthesis of a hexakis-alkylated hexa(terphenyl)benzene derivative 31 from the corresponding bis(terphenyl) acetylene (32). The peripheral tert-alkyl substituents serve to solubilize the molecule. 

The formation of resin-bound tert.-alkyl carbamates for anchoring of amines was recently described [209a]... 

This and the 4-nitrobenzoates of homologous tert-alkyl hydroperoxides explode in contact with flame. 

Addition of disilanes to isocyanides is catalyzed by palladium complexes, giving A-substituted bis(silyl)imino-methanes (Equation (53)).132 A wide range of isocyanides including aryl isocyanides and alkyl isocyanides can take part in the reaction. However, it is important to note that tert-alkyl isocyanides hardly undergo the bis-silylation reaction. This low reactivity of / r/-alkyl isocyanides allows their use as spectator ligands in the catalytic bis-silylations. 

The addition of the neutral silylborane to carbon-carbon triple bonds, in which both the boron and silicon groups were retained in the products, was achieved in 1996 by using palladium catalysts.217 Although, in the preliminary report, tert-alkyl isocyanide was used as the ligand on palladium, it was later reported that conventional phosphine... 

Alkyl orthophosphate triesters, 79 41 terteAlkyl peroxycarbamates, decomposition of, 78 486 Alkyl peroxyesters, 78 478-487 chemical properties of, 78 480 487 physical properties of, 78 480 primary and secondary, 78 485 synthesis of, 78 478-480 synthetic routes to, 78 479 tert-Alkyl peroxyesters, 78 480 84, 485 as free-radical initiators, 74 284-286 properties of, 78 481-483t uses of, 78 487 Alkylperoxy radical, 74 291 Alkyl phenol ethoxylates, 8 678, 693 ... 

Free-radical initiators, 74 274-311 tert-alkyl hydroperoxides, 74 290-291 tert-alkyl peroxyesters, 74 284-286 azo compounds, 74 293-296 carbon-carbon initiators, 74 296-297 chemical methods for radical generation, 74 299... 

We concluded, therefore, that in sufficiently pure alkyl halide solvents the tert-alkyl tetrahaloaluminates are stable electrolytes and that previous failures to produce them, and the consequent legend of the instability of tcrt-alkyl carbenium ions, arose from the use of inappropriate and insufficiently rigorous experimental techniques. On this basis it seems highly probable that in the polymerised solutions the cations R+ partaking in reaction (viii) were also original ions, i.e., 2 at the end of a live chain and 3 and 4 formed by alumination of a terminal double bond, and not derived ions formed by degradative reactions of monomer or polymer. 

In the case of acyltellurides bearing sec- and tert-alkyl substituents, the decarboxylation of CO from the acyl radical competes with the imidoylation. Such a drawback is avoided by conducting the reaction under CO pressure (50 atm). 

F and B NMR spectroscopy. The rate of propene polymerisation with this system was only three times faster than that of 1-hexene. This slow rate contributes to the high regioselectivity of the polymerisation no 2,1-propene misinsertions were detected. H and NMR spectroscopy also provided information about the chain termination mechanism here this occurred by p-H elimination in a first-order process. Polymer chain-end epimerisation, i.e. chirality inversion at the P-carbon of the polymer chain (Scheme 8.31), proceeded via a zirconium tert-alkyl (rather than tt-allyl) intermediate [96c]. 

Die Reaktion von Trichloramin mit tert.-Alkyl-chloriden in Dichlormethan in Gegenwart von Aluminiumchlorid fuhrt in einigen Fallen zur Bildung der entsprechenden tert.-Alkyl-amine in hohen Ausbeuten1. 

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