Diisobutylaluminum hydride activation

The milder metal hydnde reagents are also used in stereoselective reductions Inclusion complexes of amine-borane reagent with cyclodexnins reduce ketones to opucally active alcohols, sometimes in modest enantiomeric excess [59] (equation 48). Diisobutylaluminum hydride modified by zmc bromide-MMA. A -tetra-methylethylenediamme (TMEDA) reduces a,a-difluoro-[i-hydroxy ketones to give predominantly erythro-2,2-difluoro-l,3-diols [60] (equation 49). The three isomers are formed on reduction with aluminum isopropoxide... 

An alternative access to murrayanine (9) was developed starting from the mukonine precursor 609. The reduction of the ester group of 609 using diisobutylaluminum hydride (DIBAL) afforded the benzylic alcohol 611. In a one-pot reaction, using very active manganese dioxide, 611 was transformed to murrayanine (9) (574) (Scheme 5.36). 

Preparation of (—)-Citronellol from Optically Active Pinenes. (+)-ci5-Pinane is readily synthesized by hydrogenation of (+)-0 -pinene or (+)-/3-pinene, and is then pyrolyzed to give (+)-3,7-dimethyl-l,6-octadiene. This compound is converted into (-)-citronellol (97% purity) by reaction with triisobutylalumi-num or diisobutylaluminum hydride, followed by air oxidation and hydrolysis of the resulting aluminum alcoholate [50]. 

Polystyrene-bound carboxylic esters have been reduced with diisobutylaluminum hydride or lithium aluminum hydride. Use of the latter reagent can, however, lead to the formation of insoluble precipitates, which could readily cause problems if reactions are performed in fritted reactors. An alternative procedure for reducing carboxylic esters to alcohols involves saponification, followed by activation (e.g. as the mixed anhydride) and reduction with sodium borohydride (Entries 10 and 11, Table... 

When the bulkier, branched aluminum compounds such as triisohexyl-aluminum and diisobutylaluminum hydride were used as cocatalysts, we found (Figure 3) the same polymerization pattern as before with the tri-n-alkylalumi-nums. The polymer yields at optimum Al/Ti ratio, though, are significantly higher with these systems as compared to the yields obtained with the most active unaged /i-alkylaluminum preparations. 

By comparison with triisobutylaluminum and diisobutylaluminum hydride, diisobutylaluminum chloride required higher Al/Ti mole ratios for good activity, at least 2.0 and above (Figure 4). This must be owing, at least in part, to the lower active aluminum—carbon bond content of the halide. The halide system was also considerably less active over the entire Al/Ti range tested as compared to the corresponding triisobutylaluminum catalysts. 

Synthesis of P-Keto Sulfoxides. Optically active p-keto sulfoxides are very useful building blocks (eq 4) because they can be stereoselectively reduced to afford either diastereomer of the corresponding p-hydroxy sulfoxide under appropriate conditions (Diisobutylaluminum Hydride or Zinc ChloridefDlBALf and thus give access to a wide variety of compounds chiral carbinols by desulfurization with Raney Nickel or LithiumJethyhmme ini the case of allylic alcohols epoxides via cyclization of the derived sulfonium salt butenolides by alkylation of the hydroxy sulfoxide 1,2-diols via a Pummerer rearrangement followed by reduction of the intermediate. ... 

With few exceptions, organometalUcs add only once to nitriles (Section 8.6.4). Only if there is a very strong Lewis acid present to activate the anionic intermediate of the first nucleophilic attack will a second addition take place. An example of this second addition is the reduction of nitriles with LiAlH4, which proceeds all the way to the amine (Section 8.6.3). The AIH3 formed from the initial reduction acts as a Lewis acid to catalyze the second addition. This second addition can be prevented by using one equivalent of a less reactive aluminum hydride like LiAlH(OEt)3 or diisobutylaluminum hydride, [(CH3)2CHCH2l2AlH. The reactions in the acidic water workup are the reverse of imine formation (Section 10.5.2). 

Both 7 and 9 are procatalysts. The active catalyst, which is likely to be a copper(I) monochelate, is generated by heating in the presence of the diazocarbonyl compound at ca. 60-80 °C for a few minutes, by reduction with phenylhydrazine (9 ) or an alkylhydrazine (7 ), or by treatment with ca. 0.25-0.5 equivalents of diisobutylaluminum hydride. ... 

Complex hydrides have been used rather frequently for the conjugate reduction of activated dienes . Just and coworkers found that the reduction of a,fi-unsaturated ketene S,S-acetals with lithium triethylborohydride provided mixtures of 1,4- and 1,6-reduction products which were transformed into enals by treatment with mercuric salts (equation 27). Likewise, tetrahydro-3//-naphthalen-2-ones can be reduced with L-Selectride to the 1,6-reduction products this reaction has been utilized in the stereoselective synthesis of several terpenes, e.g. of (/J)-(—)-ligularenolide (equation 28) . Other methods for the conjugate reduction of acceptor-substituted dienes involve the use of methylcopper/diisobutylaluminum hydride and of the Hantzsch ester... 

The objective of this chapter is to examine the basic research on diene (butadiene, isoprene, and piperylene) polymerisation with the LnHalj-nL-AlRj (Ln = lanthanide, Hal = halogen, ligand (L) = tributyl phosphate (TBP), AlRj = triisobutylaluminum and diisobutylaluminum hydride) catalytic system. The chapter will analyse the role of such factors as the electronic and geometric structure of bimetallic active centres, anti-syn and 7t-o-transitions of the terminal units of the growing polymer chains and the nature of the lanthanide, diene, and organoaluminum component in the mechanism of stereoregulation. 

Magnesium turnings (0.12 g, 5.0 mmol) were placed in a dry Schlenk flask equipped with a magnetic stirrer and a septum under argon. LiCl (5.0 mL, 0.5 m in THF, 2.5 mmol) was added, and the magnesium was activated with diisobutylaluminum hydride (0.2 mL, 0.1 m in THF, 0.02 mmol). The resulting mixture was stirred for 5 min and then cooled to 0 °C. 5-Bromo-2-chloropyridine (0.39 g, 2.0 mmol) was then added in one portion, and the reaction mixture was stirred for 30 min at 0 °C. 

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