Alkylative cleavage

Oxetane, 2-(o -chlorobenzyl)-2-phenyl-X-ray crystal structure, 7, 366 Oxetane, 3-chloromethyl-3-ethyl-ring strain, 7, 370-371 Oxetane, 2-(o-chlorophenyl)- H NMR, 7, 367 Oxetane, 2-cyano-synthesis, 7, 391-392 Oxetane, 2-cyano-3,3-dimethyl-2-phenyl-thermolysis, 7, 372 Oxetane, 2,2-dialkoxy-synthesis, 7, 396 Oxetane, 2,2-dialkyl-isomerization, 7, 377 Oxetane, 3,3-dialkyl-alkylative cleavage, 7, 381 polymers, 7, 382 Oxetane, 2-diethylamino-synthesis, 7, 390 Oxetane, 3,3-difluoro-molecular dimensions, 7, 365 Oxetane, 2,2-dimethyl-mass spectra, 7, 368-369 photolysis, 7, 373 synthesis, 7, 393 Oxetane, 2,3-dimethyl- H NMR, 7, 366 thermolysis, 7, 372 Oxetane, 2,4-dimethyl-mass spectrum, 7, 369... 

Oxetane, 2-methoxy-3,3-dimethyl-hydrolysis, 7, 379 Oxetane, 2-methyl-alkylative cleavage, 7, 381 conformation, 7, 365 H NMR, 7, 366 methanolysis, 7, 379 molecular dimensions, 7, 365 reactions... 

Molecular ions are usually intense for low-molecular weight compounds. Alkyl cleavage with the charge remaining on the unsaturated portion is very often the base peak. A series of fragment ions with m/z 41, 55. 69, 83, and so forth are characteristic. Methods are available to locate the position of the double bond in aliphatic compounds.1... 

The term acid catalysis is often taken to mean proton catalysis ( specific acid catalysis ) in contrast to general acid catalysis. In this sense, acid-catalyzed hydrolysis begins with protonation of the carbonyl O-atom, which renders the carbonyl C-atom more susceptible to nucleophilic attack. The reaction continues as depicted in Fig. 7. l.a (Pathway a) with hydration of the car-bonium ion to form a tetrahedral intermediate. This is followed by acyl cleavage (heterolytic cleavage of the acyl-0 bond). Pathway b presents an mechanism that can be observed in the presence of concentrated inorganic acids, but which appears irrelevant to hydrolysis under physiological conditions. The same is true for another mechanism of alkyl cleavage not shown in Fig. 7.Fa. All mechanisms of proton-catalyzed ester hydrolysis are reversible. 

Fig. 7.1. a) Specific acid catalysis (proton catalysis) with acyl cleavage in ester hydrolysis. Pathway a is the common mechanism involving a tetrahedral intermediate. Pathway b is SN1 mechanism observed in the presence of concentrated inorganic acids. Not shown here is a mechanism of alkyl cleavage, which can also be observed in the presence of concentrated inorganic acids, b) Schematic mechanism of general acid catalysis in ester hydrolysis. 

Fig. 7.2. a) The most common mechanism of base-catalyzed ester hydrolysis, namely specific base catalysis (HCT catalysis) with tetrahedral intermediate and acyl cleavage. Not shown here are an W mechanism with alkyl cleavage observed with some tertiary alkyl esters, and an 5n2 mechanism with alkyl cleavage sometimes observed with primary alkyl esters, particularly methyl esters, b) Schematic mechanism of general base catalysis in ester hydrolysis. Intermolecular catalysis (bl) and intramolecular catalysis (b2). c) The base-catalyzed hydrolysis of esters is but a particular case of nucleophilic attack. Intermolecular (cl) and intramolecular (c2). d) Spontaneous (uncatalyzed) hydrolysis. This becomes possible when the R moiety is... 

Since no bond to C is broken, no racemization occurs. However, with 3° alcohols, there is an S l O—alkyl cleavage,... 

A convenient synthesis of unsaturated nitriles by a stereospecific alkylative cleavage of pyridine ring via borate process has been reported. Namely, the reaction of 2-bromo-6-lithiopyridine with trialkylboranes affords 5-alkyl-5-dialkylboryl-2-(25--4-(E)-pentadienenitriles (28), which are versatile intermediates for the preparation of 5-alkyl-2-(Z)-4-(E)-pentadienenitriles (29), 5,5-dialkyl-4-pentenenitriles (SO), and 5,5-dialkyl-2,4-pentadienenitriles (SJ), as depicted in Eq. 65 . 

Reactions of compounds containing more than one R group proceed stepwise, allowing intermediate products to be obtained if a deficiency of HX is used [e.g., Eq. (i)]. Rates of bond scission vary also, usually the ease of cleavage is M—aryl>M—alkyl. Cleavage of nonmetal element-C bonds with protonic acids can occur ... 

The solvolytic reactions of a-metallocenylcarbinyl acetates, which proceed by an SnI mechanism involving 0-alkyl cleavage, are characterized by their extremely high rates and by their stereoselectivity. The former aspect is well-documented in Table I, in which the kinetic results of Richards and Hill (23, 24, 40) are summarized. 

The AalI reaction (acid-catalysed, alkyl cleavage, unimolecular) is of the Sn 1 type... 

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