Ketones from isomerisation

In fact, a similar intramolecular cyclisation was studied by Reusch [11] and he found a remarkable methyl substituent effect on the aldol equilibrium. Starting from the cis-decalones 25 (easily prepared from the Wieland-Miescher ketone), in which the angular methyl group prevents isomerisation to the more stable trans-decalone, it was found that other methyl groups may exert profound but less... 

The method has been used for the preparation of dihalides, e.g., 1,9-dichlorononane (93%) unsaturated halides, e.g., 11-undecylenyl chloride (83%) halo ethers, e.g., /3-ethoxyethyl chloride (80%) halo ketones, e.g., desyl chloride (79%) halo esters, e.g, methyl a-chloropropionate (71%) halo cyanides, e.g., phenylchloroacetonitrile (80%) and aminoalkyl halides,An interesting isomerisation has been observed in liberating 2-diethylamino-l-chloropropane from its hydrochloride salt l-diethylamino-2-chloropropane is formed. ... 

Another important side reaction for both alcohols was isomerization. It is therefore proposed that the alkene is formed mainly from the cis-alcohol and that at low temperatures the trans-alcohol can only be dehydrated if it is first isomerised to the cis-alcohol via an MPVO transition-state. Comparing the deactivation of the Ti-beta catalyst in the oxidation (Fig. 5) and reduction reactions (Fig. 3) shows that the deactivation is more pronounced during oxidative conditions. This is probably caused by the high amount of ketones present, which easily form aldol condensates which may plug the zeolite chaimels, thus inhibiting access to the micropore system. 

The photo-Nazarov cyclisation of l-cyclohexenyl phenyl ketone (285) yields the hexahydrofluorenone (286). Schaffner s group has examined the mechanism of this reaction and have found evidence for some novel intermediates. They propose that the excited state of (285) decays by cis-trans isomerisation of the cyclohexenyl double bond the tx-ans-cyclohexenyl derivative (287) cyclises to the oxallyl species (288) which collapses to the relatively stable enol (289) or reacts with accumulated (289) to give the isolable enol dimer (290). When the ketone derived from (290) is photolysed it gives back (289) along with (286). The enol (290) and its corresponding ketone were both isolated and characterised, while (287) and (288) were trappable with cyclopentadiene. The enol (289) was observable by H-NMR before it ketonised and gave the isolated product (286). 

Another potential area of application of FTIR spectroscopy is in the determination of the oxidative status or stability of an oil. Autoxidation is a major deteriorative reaction affecting edible fats and oils, and it is of major concern to processors and consumers from the standpoint of oil quality, as the oxidative breakdown products cause marked off flavours in an oil. A wide range of end products are associated with the autoxidative deterioration of fats and oils, the most important being hydroperoxides, alcohols, and aldehydes. Moisture, hydrocarbons, free fatty acids and esters, ketones, lactones, furans, and other minor products may also be produced, with the free fatty acids becoming more important in thermally stressed oils. In addition, there is significant cis to trans isomerisation and conjugation of double bonds in the hydroperoxides formed as an oil oxidises. 

Allenyl-ketones pre-synthesised, or prodnced in situ from palladium(O)- or copper(I)-catalysed isomerisation of conjugated or non-conjugated ° alkynyl-ketones, can be cyclised to fnrans. The ring closure can be effected with palladium " or gold " catalysis. Acylation of silylallenes leads to a fnran directly. ... 

Comparable acid- (or Lewis acid) -catalysed ring closures of 2-arylthio- and 2-aryloxy- -ketones, and -2-arylthio- and 2-aryloxyacetyl- chlorides lead to 3-substituted heterocycles and 3-oxygenated heterocycles, respectively. It is possible to combine the preparation of the arylthio-ketone and the ring closure steps utilising two solid-supported reagents in a one-pot procedure, as illustrated. Formation of 3-aryl-benzothiophenes by this route can be complicated by partial or complete isomerisation to the 2-aryl-heterocycle,however using boron trifluoride as the Lewis acid produces only the 3-aryl-isomer. 3-Tosylamino-benzofurans can be prepared from aryl glyoxal hydrates. ... 

Oxime acetates or benzoates afford their parent ketones on triplet-sensitised photolysis, or the amides (lactams) by direct photo-isomerisation. Both products probably result from further reactions of an intermediate oxaziran (Scheme 31),... 

As seen in Chapter 6, Figure 6.33, the acid catalysed isomerisation of thujopsene (P17.1) leads to the olefin (P17.2). Acylation of (P17.2) gives a ketone with an excellent cedarwood odour. The relevant part of Figure 6.33 is reproduced below as Figure P17. The olefins (P17.10) and (PI7.11) are also present in the crude isomerisation mixture. Provide mechanisms to account for their formation. Hint one of them is formed from carbocation (PI7.4) and the other from (PI7.9). 

Starting from their experience in manufacturing /3-ionone, Hoffmann-La Roche initially favoured acetylene as the universal building block for further syntheses. The reaction of methyl vinyl ketone with lithium acetylide in ammonia gives a tertiary alcohol, which is isomerised with sulfuric acid into a mixture of the (Eland (Z)-isomers of 3-methylpent-2-en-4-ynol. The isomers can be separated by distillation. Whereas the main component, the (Z)-isomer, is used for the production of Vitamin A, the (E)-isomer finds application in carotenoid synthesis. 

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