Cyclic ketones, formation

Practicable syntheses of four-, five, and six-membered carbocyclic rings have been achieved by reaction of a,to-di-Grignard reagents with silver(i) salts. Conversion of l,3-bis(chloromethyl)cyclopentane into norbornane was effected in 82% yield, but was the only bridged-ring synthesis reported. Stereospecific cyclic ketone formation using iron(O) compounds has been reviewed. ... 

In principle, a variety of other tandem and cascade processes terminated by trapping of acylpalladium derivatives by enolates are conceivable. In reality, examples of such processes are still very rare. One such process shown in Scheme 25 involves a cyclic carbopaUadation-cyclic ketone formation via a 5-C-exo trapping tandem process. Many additional examples of such tandem and cascade processes will be devised in efforts to develop efficient routes to bicyclic and polycyclic natural products and related compounds. 

E. Weissberger and P. Laszlo, Stereospecific Cyclic Ketone Formation with Iron (o) Anatomy of an Interligand Reaction. Accounts Chem. Res., 1976, 9, 209. 

The procedure described is essentially that of Shioiri and Yamada. Diphenyl phosphorazidate is a useful and versatile reagent in organic synthesis. It has been used for racemlzatlon-free peptide syntheses, thiol ester synthesis, a modified Curtius reaction, an esterification of a-substituted carboxylic acld, formation of diketoplperazines, alkyl azide synthesis, phosphorylation of alcohols and amines,and polymerization of amino acids and peptides. - Furthermore, diphenyl phosphorazidate acts as a nitrene source and as a 1,3-dipole.An example in the ring contraction of cyclic ketones to form cycloalkanecarboxylic acids is presented in the next procedure, this volume. 

If cyclic ketones are monosubstituted in the a-position, their rates of reaction decrease as compared to the rate for the parent ketone (9,41). More highly substituted ketones (e.g., diisobutyl ketone, diisopropyl ketone) can be caused to react using newer preparative techniques (39,43,44, see Section VII). Monosubstituted acetones often can give selfcondensation products, but the recent literature (13,39,43) contains reports of the successful formation of the enamines of methyl ketones. 

There is some spectral evidence that acylation of enamines of cyclic ketones with acid chlorides having an a-hydrogen in the presence of triethylamine proceeds via the ketene and subsequent cycloaddition (84). The intermediate cyclobutanone is then opened to give the enamino ketone which is hydrolyzed to the 2-acyl cyclohexanone. In the case of enamines of larger cyclic ketones the alternate mode of the cyclobutanone opening predominates, with the formation of ring-expanded 1,3-diketones upon... 

X0 to hydroxy compounds. Lower temperatures favor ketone formation and sterically hindered carbonyls, such as 2-thienyl t-butyl ketone, are not reduced. The sensitivity of desulfurization to steric factors is evident by the failure to desulfurize 2,5-di-i-butyl-3-acetylthiophene. The carbonyl groups of both aldehydes and ketones can be protected by acetal formation, as particularly cyclic acetals are stable during desulfurization in methanol at room temperature. " The free aldehydes give primary alcohols on desulfurization. Another method to obtain only keto compounds is to oxidize the mixtures of ketone and secondary alcohol with CrOs after the desulfurization. - Through the desulfurization of 5,5 -diacetyl-2,2, 5, 2"-terthienyl (228), 2,15-hexadecandione (229) has been obtained, which... 

Transition metal catalysis in Baeyer-Villiger oxidation of cyclic ketones with formation of lactones 98AG(E)1198. 

TMM cycloadditions to cyclic and conjugated ketones have also been reported (Scheme 2.22) [31]. The steric nature of the substrate does play a critical role in determining product formation. Thus the cyclic ketone (73) produced 55% yield of the tetrahydrofuran, but no cycloadduct could be obtained from the cyclic ketone (74). The enone (75) gave only carbonyl cycloaddition, whereas enone (76) yielded only olefin adduct. Interestingly, both modes of cycloaddition were observed with the enone (77). The ynone (78) also cycloadds exclusively at the carbonyl function [34]. 

The reaction with oximes of cyclic ketones leads to formation of lactams (e.g. 6 — 7) by ring enlargement ... 

The photolytic cleavage of cyclic ketones 14 leads to formation of a diradical species, that can undergo analogously the various reactions outlined above. The decarbonylation followed by intramolecular recombination yields a ring-contracted cycloalkane 15 ... 

The preparation of enamines of unsubstituted cyclic ketones is convenient and unambiguous in that only a single product results. Moreover, such enamines have found wide application as means of chain extension or ring formation. 

Scheme 5.1-60 The use of NaCI/AICl3 (X(AICl3) = 0.68) in the formation of cyclic ketones.

The molecular ion can be very small or nonexistent. Esters where R is greater than methyl form a protonated acid that aids in the interpretation (e.g., m/z 47, formates m/z 61, acetates m/z 75. propionates m/z 89, butyrates etc.). Interpreting the mass spectra of ethyl esters may be confusing without accurate mass measurement because the loss of C2H4 can be confused with the loss of CO from a cyclic ketone. 

Carbon dioxide 53 55). If excess C02 and polar solvents are used the carboxylation is quantitative and free of side reactions. In nonpolar solvents association phenomena favor ketone formation 55). An alternate way to get re-carboxylic polymers is to react the living sites with a cyclic anhydride 561. 

Not only do oximes undergo the Beckmann rearrangement, but so also do esters of oximes with many acids, organic and inorganic. A side reaction with many substrates is the formation of nitriles (the abnormal Beckmann rearrangement, 17-31). Cyclic ketones can be converted directly to lactams in one laboratory step by... 

Recently, it has been demonstrated that coordination vacancies on the surface metal cations are relevant to the unique redox reactivity of oxide surfaces]2]. Oxidation of fonnaldehyde and methyl formate to adsorbed formate intermediates on ZnO(OOOl) and reductive C-C coupling of aliphatic and aromatic aldehydes and cyclic ketones on 1102(001) surfaces reduced by Ar bombardment are observed in temperature-prognunmed desorption(TPD). The thermally reduced 1102(110) surface which is a less heavily damaged surface than that obtained by bombardment and contains Ti cations in the -t-3 and +4 states, still shows activity for the reductive coupling of formaldehyde to form ethene]13]. Interestingly, the catalytic cyclotrimerization of alkynes on TiO2(100) is also traced in UHV conditions, where cation coordination and oxidation states appear to be closely linked to activity and selectivity. The nonpolar Cu20( 111) surface shows a... 

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