Pentane fragmentation

The treatment of 1,2,4-triazines containing the camphor (168) or methylcyclo-pentane fragment (169) with m-chloroperbenzoic acid gives annelated 1,2,4-triazine 1-oxides 170 and 171, respectively (82JHC1201). 

The finding of preparatively available iminoboranes RB = NR some years ago opened exciting new possibilities not only in B—N chemistry, but also in coordination chemistry. The first examples of iminoborane-transition-metal complexes have now been published. The structurally completely characterized t-BuB = NBu-t adds, like its alkyne analog, to the 03(00)5 fragment as a bridging ligand. When Co2(CO)g and t-BuB = NBu-t are dissolved in pentane at 0°C, warming to RT and evaporation of unreacted iminoborane yields (t-BuBNBu-t)Co2(CO)5 (86%) as a black solid, which can be recrystallized from ether-nitromethane (1 3) ... 

B A liquid insoluble in pentane but soluble in benzene 65 i A mixture of alkyl side chains and aromatic fragments, predominantly di-aromatic. It exists either as alkyl phenols or as aromatic fragments attached to phenol by methylene bridges It also contains other oxygen functiona groups... 

The work of Kikuchi et al. (123) with silica-supported catalysts also shows the high tendency of iron (370°-400°C), cobalt (330o-360°C) and nickel (330°-370°C) to catalyze fragmentation (of n-pentane) to methane. This work also showed that with cobalt and nickel, the extent of methane formation tended to decrease with increasing hydrogen partial pressure. Some data are listed in Table XII. 

Earlier we reported that Ni-pentane matrices upon warming from -196°C yielded tiny Ni particles that incorporated substantial organic material from fragmented pentane (3JO. The amount of organic material (mainly fragments) could be increased and the Ni particle sizes decreased by allowing the Ni-pentane matrix to warm slowly. 

Claisen rearrangement. As for the mechanism, the reaction begins with intramolecular cyclopropanation the resulting bicyclo[2.1.0]pentan-2-one then undergoes fragmentation to a p,y-unsaturated ketene which finally is trapped by the added alcohol to afford a p,y-unsaturated ester (Scheme 41). The intermediates could be observed in selected cases. 

In addition, 18-19% of isobutene and chloroacetylene formed via fragmentation. Photolysis of the diazirine in up to 9 M trimethylethylene in pentane led to a sharp decrease in 27 and 28 (to 32% and 8.5%), along with 40% of cyclopropanes formed via the capture of 19. However, the yield of isobutene and chloroacetylene was unchanged, indicating that these products did not stem from the carbene, but arose directly by fragmentation of its excited diazirine precursor.45... 

Formation of two bonds between a four-atom fragment and a group IV element atom provides a route to various germanium, tin and lead heterocycles, especially to 1,3-diheterametallacyclo-pentanes and -cyclopentenes. Different types of reactants and reactions are used depending on target molecule structures. 

The gross structural features, presence of a tetramic acid and E-decenoyl side chain, could be inferred from NMR studies. Methanolysis (HCl/MeOH) of 47 and pentane extraction of the quenched reaction mixture gave two compounds that were determined to be the methyl esters of decenoic acid and N-(2-decenoyl)leucine. The nature of the 3-acyl tetramic acid was deduced from the identification of 48 and 49 in the aqueous portion of the methanolysis reaction mixture following treatment with trifluoroacetic acid anhydride. The unusual C-C bond fragmentation under acidic conditions, and the structure of the antibiotic was confirmed by synthesis of racemic 47 [86]. The configuration at the lone chiral centre was established as R by chiral GC. The carbon NMR spectrum of 47 indicated an equilibrium between three tautomers in which the A2-pyrrolin-4-one form is preferred (60%) and the two internal tautomers (50, 51) make equal contributions (20% each). 

Apart from fragmentations, the main byproducts isolated are partially fluorinated compounds in which the remaining hydrogen atoms are attached to the most hindered carbon as demonstrated in the case of di-tert-butylmethane (l)11 and in the preparation of dimethyl bexa-fluorobicyelo[1.1.1]pentane-l,3-dicarboxylate(2, R = F). Apart from the perfluorinated products considerable amounts of polyfluoro derivatives are also obtained.12... 

It is significant that the mixture yielded propane as the major product (Table III). As noted in our earlier paper on catalytic cracking (6), the predominance of C3 fragments in the cracked products and the absence of isobutane appeared to be a unique property of erionite. Our present data indicate that this is also true for hydrocracking over a dual function erionite. The only exception was that when n-pentane alone was hydro-cracked, equimolal quantities of ethane and propane were found. This shift in product distribution in the presence of n-hexane, a second crackable component, indicated that the reaction path within the intracrystalline space was complicated. 

The nature of the C6 side-chain fragment produced depends, to some extent, on the tissue utilised and the conditions under which the experiments are carried out, but it is generally accepted that 4-methyl pentanal is formed first and that this may be oxidised to the corresponding acid or, alternatively, reduced to 4-methyl pen-tanol [29]. 

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