Aluminum 3-diketonates

Aluminum /3-diketonates have been much studied by nmr methods because of their stereochemical nonrigidity. Aluminum(III), Ga111, and Inm form stable complexes with di-, tri-, and hexadentate chelating ligands in which the metal is octahe-drally coordinated. These complexes are stable under physiological conditions. Complexes of the radioisotopes 67Ga (y, t1/2 = 3.25 d), Ga (/3+, = 68 min), and... 

A systematic study of the kinetics of vaporization of Al(acac)3 along with fluori-nated aluminum /3-diketonate complexes, Al(tfac)3 (5) and Al(hfac)3 (6), has been reported, and the saturation vapor pressures determined at 75-175°C [106]. 

This method is useful only for electropositive elements such as alkali metals, alkaline earths, and aluminum. Diketones react with these metals, in anhydrous aromatic solvents, with evolution of molecular hydrogen and formation of the metal diketonate (Equation (11)) ... 

The parent hexathiaadamantane (185) is obtained preparatively when a solution of formic acid and hydrochloric acid in nitrobenzene is allowed to stand for several weeks in a hydrogen sulfide atmosphere the product which separated is almost insoluble in all common solvents and purification presents a problem. Only large volumes of dimethyl sulfoxide at reflux serve for recrystallization.224 The reaction of thioacetic acid with formic acid in the presence of zinc chloride gives tetramethyl-(186), monomethyl-, dimethyl-and trimethylhexathiaadamantane derivatives (187).225 Other variations include the reaction of thioacetic acid with a /i-diketone,226 and the use of boron trifluoride227 or aluminum chloride as a catalyst.228... 

For example, the reaction of nitronates (123) with a zinc copper pair in ethanol followed by treatment of the intermediate with aqueous ammonium chloride a to give an equilibrium mixture of ketoximes (124) and their cyclic esters 125. Heating of this mixture b affords pyocoles (126). Successive treatment of nitronates (123) with boron trifluoride etherate and water c affords 1,4-diketones (127). Catalytic hydrogenation of acyl nitronates (123) over platinum dioxide d or 5% rhodium on aluminum oxide e gives a-hydroxypyrrolidines (128) or pyrrolidines 129, respectively. Finally, smooth dehydration of a-hydroxypyrrolidines (128) into pyrrolines (130f) can be performed. 

Selective reduction of ketones.1 This reagent can be used to effect selective reduction of the more hindered of two ketones by DIBAH or dibromoalane. Thus treatment of a 1 1 mixture of two ketones with 1-2 equiv. of 1 results in preferential complexation of the less hindered ketone with 1 reduction of this mixture of free and complexed ketones results in preferential reduction of the free, originally more hindered, ketone. An electronic effect of substituents on a phenyl group can also play a role in the complexation. This method is not effective for discrimination between aldehydes and ketones, because MAD-complexes are easily reduced by hydrides. MAD can also serve as a protecting group for the more reactive carbonyl group of a diketone. The selectivity can be enhanced by use of a more bulky aluminum reagent such as methylaluminum bis(2-f-butyl-6-( 1,1-diethylpropyl)-4-methylphenoxide). 

Synthesis ofLysergic Acid, By reacting N-benzoyl-3-(B-carboxyethyl)-dihydroindole (see JCS, 3158 (1931) for the preparation of this compound) with thionyl chloride, followed by aluminum chloride gives l-benzoyl-5-keto-l,2,2a,3,4,5-hexahydrobenzindole. This is then brominated to give the 4-bromo-derivative, which is converted to the ketol-ketone by reacting with methylamine acetone ethylene ketol. This is then hydrolized by acid to yield the diketone and treated with sodium methoxide to convert it to the tetracyclic ketone. Acetylate and reduce this ketone with sodium borohydride to get the alcohol, which is converted to the hydrochloride form, as usual. 

Two years later, Craig and Robinson attempted an alternative synthesis of 8 with a more symmetrical pathway starting from derivatives of fluoranthene. Cycliza-tion of fluoranthene-7,10-diacetic acid 14 was attempted to produce diketone 15, expected to enolize to the dihydroxycorannulene 16. Unfortunately, several attempts at cyclization failed, including anhydrous hydrofluoric acid, concentrated sulfuric acid, and polyphosphoric acid. Friedel-Crafts cyclization of the corresponding acid chloride of 14 with aluminum or stannic chloride was similarly unsuccessful. However, although Craig and Robinson were not successful, they developed a convenient synthesis of 7,10-disubstituted fluoranthenes which turned out later to be of premium importance in a new, successful synthesis of corannulene. 

In the following year, this method was also applied to the total synthesis of tjipanazole FI (371) (784). For this synthesis, the required bisindole 1444 was obtained starting from 5-chloroindole (1440) in three steps and 47% overall yield. Acylation of 1440 with oxalyl chloride led to the glyoxylic acid chloride 1441. Transmetalation of indolylmagnesium bromide with zinc chloride, followed by addition of the acid chloride, provided the ot-diketone 1443. Exhaustive reduction of 1443 with lithium aluminum hydride (LiAlFl4) afforded the corresponding bisindolylethane 1444. Executing a similar reaction sequence as shown for the synthesis of tjipanazole F2 (372) (see Scheme 5.243), the chloroindoline (+ )-1445 was transformed to tjipanazole FI (371) in two steps and 50% overall yield (784) (Scheme 5.244). 

Ethoxypenta-l, 3-diene underwent the Diels-Alder reaction withp-benzoquinone to give the cis-fused diketone I. Selective catalytic hydrogenation (Ni) of I, followed by reduction with lithium aluminum... 

Reactions of 4,7-phenanthroline-5,6-dione have been the subject of considerable study. It is reduced to 5,6-dihydroxy-4,7-phenanthroline by Raney nickel hydrogenation226,249 or by aromatic thiols in benzene,262 and oxidized by permanganate to 3,3 -bipyridyl-2,2 -dicarboxylic acid.263 It forms bishemiketals with alcohols226 and diepoxides with diazomethane.226 The diepoxides by reaction with hydrochloric acid form diols of type 57, R = Cl, which on oxidation with lead tetraacetate give 3,3 -bipyridyl diketones of type 58, R = Cl. Methyl ketones of type 58, R = H, are also obtained by lead(IV) acetate oxidation of the diol 57, R = H, obtained by lithium aluminum hydride reduction of 57, R = Cl. With phenyldiazomethane and diphenyldiazomethane the dione forms 1,3-dioxole derivatives,264,265 which readily hydrolyze back to the dione with concomitant formation of benzaldehyde and benzophenone, respectively. 

An efficient synthesis of ( )-quebrachamine is based on the construction of a suitable precursor via ring cleavage of an a-diketone monothioketal (810) (80JCS(P1)457). This monothioketal, available from 4-ethoxycarbonylcyclohexanone ethylene ketal, was fragmented to the dithianyl half ester (811) with sodium hydride in the presence of water. Reaction of (811) with tryptamine and DCC provided an amide which was converted to the stereoisomeric lactams (812) on hydrolysis of the dithiane function. Reduction of either the a- or /3-ethyl isomer with lithium aluminum hydride followed by conversion of the derived amino alcohol to its mesylate produced the amorphous quaternary salt (813). On reduction with sodium in liquid ammonia, the isomeric salts provided ( )-quebrachamine (814 Scheme 190). 

In the above examples, the nucleophilic role of the metal complex only comes after the formation of a suitable complex as a consequence of the electron-withdrawing effect of the metal. Perhaps the most impressive series of examples of nucleophilic behaviour of complexes is demonstrated by the p-diketone metal complexes. Such complexes undergo many reactions typical of the electrophilic substitution reactions of aromatic compounds. As a result of the lability of these complexes towards acids, care is required when selecting reaction conditions. Despite this restriction, a wide variety of reactions has been shown to occur with numerous p-diketone complexes, especially of chromium(III), cobalt(III) and rhodium(III), but also in certain cases with complexes of beryllium(II), copper(II), iron(III), aluminum(III) and europium(III). Most work has been carried out by Collman and his coworkers and the results have been reviewed.4-29 A brief summary of results is relevant here and the essential reaction is shown in equation (13). It has been clearly demonstrated that reaction does not involve any dissociation, by bromination of the chromium(III) complex in the presence of radioactive acetylacetone. Furthermore, reactions of optically active... 

Although formally involving the reaction with a C—H bond, metal alkoxides will react with /1-diketones and / -keto esters to form six-membered chelates and alcohols. Hence the acetyl-acetonate (acac) derivatives of aluminum can be obtained (equation 63).238... 

Related to jS-diketones are metalla-/ -diketones, whose distinctive chemistry is a recent development. In these, the methine group of a conventional diketonate is replaced with an organometallic moiety such as m-Mn(CO)4, m-Re(CO)4, /<2c-Mn(CO)3(RNC) or C5H5Fe(CO).519 Exemplary is Al Mn(MeCO)2(CO)4 3, which is prepared in a two-step synthesis. Addition of methyllithium to Mn(CO)5COMe forms Li[Mn(MeCO)2(CO)4] which, when treated with aluminum chloride, provides the tris(chelate) compound.520 An X-ray study showed that the MnC202Al ring is essentially planar with Mn—C(acyl) bond distances indicative of a bond order of ca. 1.2. The O—O bite distance, 2.73 A, is about the same as that of acetylacetonate in Al(MeCOCHCOMe)3.521 As in the... 

In contrast to titanium(IV) tetrachloride, which causes polymerization of a,3-unsaturated esters, aluminum triflate88 or aluminum-impregnated montmorillonite87b are excellent promoters of silyl ketene acetal additions to a,(3-unsaturated esters (Scheme 35). Similarly, the addition of silyl ketene acetals and enol silyl ethers to nitroalkenes, followed by Nef-type work-up, affords y-keto esters (216) and y-di-ketones (218), respectively (Scheme 35).89a>89b Mechanistically, the y-diketones (218) arise from Nef-type hydrolysis of an initial nitronate ester (217).89e 89d Mukaiyama reports that SbCls-Sn(OTf)2 catalyzes diastereoselective anti additions of silyl ketene acetals, silyl thioketene acetals and enol silyl ethers to a,(3-unsaturated thioesters (219).90... 

Aluminum oxide sols are successfully used for application of films [1794, 1793], such as high area films for hybrid circuits [1236]. The same technique was used for the preparation of J-A1203 (NaAlnO,7) in this case alcoholic solutions of NaOR were added to aluminum alkoxide solutions [1795, 1038]. To increase the stability of sols, aluminum alkoxides are frequently modified with acetic acid [1570] or (3-diketones [1659]. Alumina sheets are commercially produced by the sintering of high-purity fine A1203 powders prepared by hydrolysis of modified Al(OPr )3 [1236]. To prepare powders with spherical species from dilute solutions, hydroxopropylcellulose was added to prevent... 

On treatment with concentrated hydrochloric acid and aluminum amalgam, l-telluracyclohexane-3,5-diones decompose with elimination of tellurium. Their chemical behavior is determined by the presence of the dicoordinate tellurium center and two carbonyl groups in their molecules. As cyclic diketones, compounds 12 readily form oximes and dioximes under treatment with hydroxylamine. The former reaction is preferably carried out in dilute acetic acid solution, whereas the latter is carried out in basic... 

Figure 6. Reflection spectrum of an oxidized aluminum film exposed to 0.01 OM 2,4-pentanedione in ethanol. Also shown are the peak positions for transmission spectra of the pure diketone (AcAcH) and the aluminum complex (Al(AcAc)s).

The main basic difference between these two wide classes of compounds is described as follows p-diketonate molecules are associated in the condensed phase (crystalline) and, in a number of cases, also in solution, while the pyrazolyl-borates keep themselves as monomers. In addition to boron, ligands 232 and 233 may contain aluminum (E = A1) and gallium (E — Ga) [443-445],... 

With certain types of compounds this method of reduction fails. In general, /3-keto esters (XX) and /3-diketones which are capable of enoliza-tion form the aluminum salt of the enolic form and aje not reduced. However, if there are no enolizable hydrogens (XXI), reduction proceeds smoothly. If a phenolic ketone or a keto acid forms a salt which is... 

The following tables are intended to include all the reductions with aluminum alkoxides which were reported prior to February, 1943, although some examples doubtless have been overlooked. Table I lists the reduction of aldehydes, which have been subdivided into (a) aliphatic aldehydes and (b) alicyclic and aromatic aldehydes. Table II lists the reduction of ketones, which have been classified as (a)-satu-rated and unsaturated aliphatic ketones, (b) aromatic ketones, (c) alicyclic ketones, (d) unsaturated alicyclic and aromatic ketones, (e) a- — halogen substituted ketones, (f) diketones, (g) protected diketones, (h) alcoholic and phenolic ketones (and ethers or esters of these), and (i) keto esters. 

Diketones are synthesized by Claisen condensation of appropriate acetyl methyl ketone and ethyl perfluoroalkyl carboxylate. For example, 4,4/-bis(l",l,/,l//,2//,2",3//,3//-heptafluoro-4//,6//-hexanedion-6"-yl)-chlorosulfo-o-terphenyl (BHHCT) was synthesized from o-terphenyl by three step reactions (scheme 3 (Yuan et al., 1998a, 1998b)). The o-ter-phenyl are acetylated by acetyl chloride with anhydrous aluminum chloride as a Lewis acid and 4,4 -diacetyl-e>-terphcnyl is obtained. Then, the 4,4/-diacetyl-o-terphenyl is reacted with perfluoropropionic acid ethyl ester with sodium methoxide as a base. Finally, 4,4,-bis(l", 1",l//,2,2,3,/,3"-heptafluoro-4//,6"-hexanedion-6//-yl)-o-terphenyl is chloro-sulfonylatcd by chlorosulfonic acid to form BHHCT. 

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