Aluminium t-butoxide

Oppenauer reaction is oxidation of secondary alcohols to ketones using aluminium t-butoxide... 

Normally, Oppenauer oxidations are performed employing Al3+ cations as catalyst because aluminium alkoxides possess a good balance of a desired high hydride transfer capability versus a low propensity to promote undesired base-induced reactions, like aldol condensations and Tischtschenko reactions. In the reaction, as originally described by Oppenauer, aluminium t-butoxide is used as catalyst,4 because its high basicity allows a very favourable equilibrium towards the formation of the aluminium alkoxide of the alcohol whose oxidation is desired. However,... 

Allylic sulfones and a, /5-unsaturated sulfones are known to be in equilibrium314-319. Allylic sulfones, such as 242, isomerize to a, /5-unsaturated sulfones 243 upon treatment with a catalytic amount of potassium t-butoxide in dry THF. The a, /5-unsaturated sulfones can be converted to the corresponding olefins upon desulfonation with sodium amalgam320 or aluminium amalgam294,321. Since treatment of allylic sulfones with potassium-graphite gives 2-alkenes, alkylation of allylic sulfones and subsequent desulfonation is a useful process for the synthesis of olefins, as shown in Scheme 6. 

The only solid acidic catalyst which has given high polymers at an appreciable rate at low temperatures, and which has been studied in some detail, is that described by Wichterle [41, 42]. This was prepared as follows A 10 per cent solution in hexane of aluminium tri-(s- or t-butoxide) was saturated with boron fluoride at room temperature, and excess boron fluoride was removed from the precipitate by pumping off about half the hexane. Two moles of boron fluoride were absorbed per atom of aluminium, and butene oligomers equivalent to two-thirds of the alkoxy groups were found in the solution the resulting solid had hardly any catalytic activity. When titanium tetrachloride was added to the suspension in hexane, an extremely active catalyst was formed but the supernatant liquid phase had no catalytic activity. The DP of the polymers formed by the catalyst prepared from the s-butoxide was much lower than that of polymers formed with a catalyst prepared from the r-butoxidc. 

Secondary alcohols may be oxidised to the corresponding ketones by the use of an aluminium alkoxide, frequently the t-butoxide, in the presence of a large excess of acetone (the Oppenauer oxidation). The reaction involves an initial alkoxy-exchange process followed by a hydride ion transfer from the so-formed aluminium alkoxide of the secondary alcohol by a mechanism analogous to that of the Meerwein-Ponndorf-Verley reduction (see Section 5.4.1, p. 520). 

The n.m.r. characteristics of the isopropylidene acetals of the four possible types of ring A primary, secondary 1,3-glycol systems, exemplified by serratriol (178), lycoclavanol (179), methyl hederagenate (180), and methyl 3-epihederagenate (181), have been tabulated, and provide a useful means of differentiation.132 The reactions of the primary monotosylates of these four types provide further confirmation of stereochemistry.133 With potassium t-butoxide the cis types (178) and (181) afforded oxetans whereas the trans types (179) and (180) were converted into A-seco-aldehydes (182). Appreciable amounts of alkyl oxygen fission products were obtained on lithium aluminium hydride reduction of the monotosylates of (178), (180), and (181), presumably via participation of the 3-hydroxy-group, e.g. (183). 

The secondary alcohols are oxidized to ketones by refluxing with aluminium isopropoxide, A1[0CH(CH3)2]3 [or Al(0-iPr)3], or potassium t-butoxide, KOC(CH3)3 [or KO-t-Bu]. A ketone such as acetone used in the reaction as refluxing agent is reduced to alcohol, 2-propanol. The reaction is known as the Oppenauer oxidation. The reverse reaction known as the Meerwein-Ponndorf-Verly reduction is the reduction of ketones to alcohols in the presence of alcohol such as 2-propanol. Potassium fert-butoxide can be used for the oxidation of primary alcohols. Aluminium isopropoxide in acetone is particularly used for... 

A cyclopentane aldehyde (297) is obtained when verbenone epoxide (298) is treated with zinc bromide. The presence of pinene in the products is difficult to explain, and the difference in products obtained with aluminium chloride (Vol. 1, p. 45) is remarkable. When the toluene-p-sulphonylhydrazone of the epoxide (298) is treated with potassium t-butoxide, both isomers of the cyclobutyl-acetylene (299) are obtained in an Eschenmoser fragmentation. ... 

H, OH) when treated with lithium aluminium hydride.The cis-fused hydroxy-tosylate (114 X = OTs, Y = H) gave ketone (115 Y = H, Z = O) exclusively when treated with potassium t-butoxide whereas its trans-fused isomer gave a mixture of (115 Y = H, Z = O) and oxetan (116). The cyclodeca-1,6-diene (117) was prepared... 

Cyclization with either aluminium tri(t-butoxide) or titanium tetra-t-butoxide gave cephems (160) and (161). 

Intramolecular palladium-catalyzed cyclization reactions have also been used to synthesize pyrazole derivatives. iV-Aryl-iV-(o-bromobenzyl)hydrazines 494 participated in a palladium-catalyzed intramolecular amination reaction to give 2-aryl-2//-indazoles 495 (Equation 101) <20000L519>. Palladium-catalyzed intramolecular C-N bond formation of iV-acetamino-2-(2-bromo)arylindolines 496, followed by hydrolysis and air oxidation in the presence of aluminium oxide, allowed the preparation of indolo[l,2-3]indazoles 498 via intermediate 497 (Scheme 58) <2002TL3577>. 3-Substituted pyrazoles have been prepared from the intramolecular cyclization of A -tosyl-iV-(l-aryl/ vinyl-1-propyn-3-yl)hydrazine and then exposme of the reaction mixture of the cyclization to potassium /i //-butoxide <1997SL959>. iV-Aryl-iV -(o-bromobenzyl)hydrazines 499 or [A -aryl-A -(t>-bromobenzyl)hydrazinato-A ]-triphenyl-phosphonium bromides 501 participated in a palladium-catalyzed intramolecular amination reaction to give 1-phenyl-l//-indazoles 500 (Scheme 59) <2001TL2937>. 

The cubane structure [M4(m3-OR)4] (Fig. 4.6) is favoured by the alkali metal tertiary butoxides (M = K, Rb, Cs) and thallium(i) alkoxides, and also related species such as [Me4Zn4(/ t-OMe)4]. Another common tetranuclear structure [M4(jti-OR)6(OR)6] (Fig. 4.7) involves one central octahedral metal bridged to three tetrahedral metals in a chiral configuration (D3). Crystalline aluminium isopropoxide was the first example established to have this structural type. ° Interestingly in the heterometallic complex [ErAl3(OPr )i2] the central position is occupied by the erbium ion in a distorted trigonal prismatic configuration. ... 

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