Ketones intramolecular acylation

Intramolecular acylation of ketones yields cyclic p diketones when the ring that is formed is five or six membered... 

Fries rearrangement.1 Rearrangement of phenyl esters with Lewis acids results in a mixture of ortho- and para-phenolic ketones. In contrast, reaction of an o-bromophenyl ester with sec-butyllithium results in exclusive formation of the orf/jo-phenolic ketone by an intramolecular acyl rearrangement.2... 

There were two more stereocenters to set. It was expected that cuprates would add to the open face of the strained cyclobutene. The control of the other stereocenter was more problematic. One solution was to prepare an a-sulfonyl lactone. To this end, the ketone was converted to the secondary carbonate. As hoped, conjugate addition was followed by intramolecular acylation, but the reaction continued to full acyl transfer, to give 10. Fortunately, desilylation of 10 proceeded with concomitant lactonization. Desulfonylation then gave 2, which could be brought to high by recrystallization. 

Although the ketone (416) gives a good yield of the pyran-4-one (417) with acetic acid (Scheme 138), the structurally related deoxybenzoin is converted into the fluorenone derivative (418) (equation 16). In the latter case intramolecular acylation occurs, presumably as a result of a favourable conformation of the carbonyl group. The former ketone cannot adopt such an array and hence is unable to cyclize in this manner (61JA193). 

Intramolecular acylation has been used frequently. Houben-Hoesch cyclization of 1 -/ -cyanoethylpyrrole (2a) gives l-oxo-2,3-dihydropyrrolizine (3a).9-17 Difficulties occur because polymerization of the nitrile (2a) can be a side reaction. Addition of boron trifluoride [3a (33%)]11 or its ethyl ether complex [3a (60-80%)]15 has been recommended. Treatment of nitrile 2a with a molten aluminum chloride-potassium chloride-sodium chloride mixture yields 70% of ketone 3a but the experimental conditions are highly critical.13 A reproducible procedure that is based mainly on Clemo s specification9,10 gave 22% of ketone 3a.17 Purification of 3a should be carried out in an efficient fume hood because it appears to induce analgesia.1 ... 

Intramolecular acylation in suitable aromatic aldehydes occurs in the presence of IPy2BF4 and HBF4 to form benzocyclic ketones.63 For example, (58) can be formed by cyclization of (57) in 74% yield. Two plausible mechanistic pathways have been suggested. 

N-Tfa- and iV-Fmoc-a-amino ketones have been synthesized56 by reaction of some N -heterocycles or benzene with chiral AM Tfa- and Fmoc-a-aminoacyl)benzotriazoles [e.g. (49)] in the presence of aluminium trichloride. Full preservation of chirality was reported. Aromatic side-chains in some of the (a-amineacyl)benzotriazole compounds gave a competitive intramolecular cyclization, again with retention of chirality [e.g. (49) to (50)]. A full report57 on the intramolecular acylation of aromatics with Meldrum s acid derivatives catalysed by metal trifluoromethanesulfonates under mild reaction conditions has appeared [e.g. (51) to (52)]. The method tolerates many functional groups and was extended to the synthesis of 1-tetralones, 1-benzosuberones and donepezil (53). 

Treatment of saturated azlactones with aromatic compounds under Friedel-Crafts conditions gives acylamino ketones in high yield (equation 46). 4-Benzyl-2-methyl-5(4H)-oxazolone undergoes an intramolecular reaction to yield an acetamidoindanone (equation 47). Friedel-Crafts reactions of 4-(arylmethylene)-5(4H)-oxazolones are complicated by the presence of an additional electrophilic centre (cf. 201) and may follow three courses. The unsaturated azlactone (189) adds benzene under the influence of aluminum chloride to form the saturated azlactone (207) in inert solvents (189) undergoes an intramolecular acylation to yield a mixture of the indenone (208) and the isoquinoline (209 Scheme 20). 

Intramolecular acylations of pyrroles and indoles are useful synthetically, for example, A-glutamyl-substituted pyrrole 94 gives 95, regioselectively, with retention of configuration, on brief treatment with methanolic hydrogen chloride or boron tribromide. A seven-membered ketone 97 was produced from 96 no cyclization onto the indole 4-position was observed <1999T4341>. 

Anionic acyl-iron complex (8) may be intercepted by ethylene, which inserts into the acyl-iron bond to produce a S-metalloketone that rearranges to an a-metalloketone (Scheme 4). Protonation affords the ethyl ketone. Intramolecular (see Intramolecular) versions of this process are known as well, and provide an approach to cychc ketones. That the cyclization is not always regioselective (see Regioselectivity) is shown in an example used in the total synthesis of ( )-aphidicolin (Scheme 5). 4i... 

Similar reactions have been carried out on acetylene.In an interesting variation, thiocarbonates add to aUcynes in the presence of a palladium catalyst to give a p-phenylthio a,p-unsaturated ester.Aldehydes add to alkynes in the presence of a rhodium catalyst to give conjugated ketones.In a cyclic version of the addition of aldehydes, 4-pentenal was converted to cyclopentanone with a rhodium-complex catalyst. An intramolecular acyl addition to an alkyne was reported using silyl ketones, acetic aid and a rhodium catalyst. In the presence of a palladium catalyst, a tosylamide group added to an alkene unit to generate A-tosylpyrrolidine derivatives. 

O. R. 1-9, C. R. Hauser and B. E. Hudson, Jr., The Acctoacetic Ester Condensation and Related Reactions lV-4, S. M. McElvain, The Acyloins 11-4, W. S. Johnson, The Formation of Cyclic Ketones by Intramolecular Acylation VIII-2, D. A. Shirley, The Synthesis of Ketones from Acid Chlorides and Organometallic Compounds of Magnesium, Zinc, and Cadmium. ... 

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