Reagents alkylaluminum

Zr-Catalyzed Enantioselective Alkylation of Alkenes with Alkylaluminum Reagents... 

VDC polymer degradation and, 25 717 2-Alkyl-alcohols. See Guerbet alcohols Alkylalkanolamines, 2 140 Alkylaluminum compounds, 2 285 Alkylaluminum halides, 2 358 Alkylaluminum reagents, in triorganotin preparation, 24 815-816 Alkyl amino acids, protonated, 17 780 Alkylaminomethanols, 12 112 AT-Alkyl amino propionates, 24 148... 

In the fourth and final chapter, Howard Haubenstock discusses asymmetric reduction of organic molecules. Within this general topic of wide and continuing interest, Haubenstock s chapter deals with chiral derivatives of lithium aluminum hydride, their preparation from suitable amino or hydroxy compounds, and their use in reducing carbonyl groups. Related reactions of the Meerwein-Ponndorf-Verley type or involving tri-alkylaluminum reagents are also presented. 

Caut/on Alkylaluminum reagents must be handled under total exclusion of atmospheric oxygen and moisture (see Example 3-28). 

Synthetic applications of the /1-pathway include conversions of the TIPS allylic azides to enones with tetrabutylammonium fluoride, ionization of the C-N3 bond with alkylaluminum reagents and capture of the TIPS enonium ions with carbon nucleophiles, and development of a procedure for y-lactamization [15-17]. Allylic azidonations of TIPS enol ethers have also been incorporated into syntheses of (+)-pancratistatin [18,19] and the core structure of lycorane [20]. 

Numerous binary and ternary diene polymerization initiator systems with neodymium as the rare-earth metal component have been designed empirically and investigated since the early discoveries in the 1960s. Commercially used neodymium-based catalysts mostly comprise Nd(III) carboxylates, aluminum alkyl halides, and aluminum alkyls or aluminum alkyl hydrides [43, 48,50-52]. Typically, the carboxylic acids, which are provided as mixtures of isomers from petrochemical plants carry solubilizing aliphatic substituents R. They are treated with the alkylaluminum reagents to generate the active catalysts in situ (Scheme 11). 

Scheme 24 Formation of a structurally characterized heterobimetallic Nd(III)/A1 complex from Nd(Oi-Pr)3 and alkylaluminum reagents. Three different types of metal environments are realized for six structurally independent neodymium cations Ndl-Nd6 [170]...

Scheme 46 Adduct formation and peralkylation with bis(trimethylsilyl)amides and tri-alkylaluminum reagents [18,190]...

Chloro-l,6-heptadienes underwent alkylation/5-exo cyclization reactions in the presence of alkylaluminum reagents catalyzed by 5 mol% FeCl3 in the presence of PPI13 or DPEphos affording 2-alkylmethylenecyclopentanes in 30-80% yield. A polar two-electron mechanism was formulated for the reaction, but radicals may be involved [88]. 

The following examples illustrate the complementary regioselectivities exhibited in the reactions using Me2CuLi and MesAl (Scheme 13). ° ° One problem which remains to be solved, however, is the proclivity of alkylaluminum reagents such as Et3Al to serve as hydride donors. ... 

Alkyl aluminum compounds are known to be radical initiators. Kabalka and coworkers reported fhe first unequivocal example of a free-radical process in which the classical organoaluminum reagent PrsAl was used in fhe presence of O2 or under UV irradiation [203]. In modern studies, modified alkylaluminum reagents enabled more practical improvement in fhe control of diastereo- and enantioselectivity in radical initiation and reactions. 

In the Zr-catalyzed enantioselective alkylation reactions discussed above, we discussed transformations that involve the addition of alkylmagnesium halides and alkylaluminum reagents to olefins. With the exception of studies carried out by Negishi and coworkers, all other processes involve the reaction of a C-C n system that is adjacent to a C-0 bond. Also with the exception of the Negishi study [Eqs. (6) and (7)], where direct olefin carbometallation occurs, all enantioselective alkylations involve the intermediacy of a metallacyclopentane (cf. Scheme 3). In this segment of our discussion, we will examine the Ni-catalyzed addition of hard nucleophiles (e.g., alkylmagnesium halides) to olefins that bear a neighboring C-0 unit. These reactions transpire by neither of the above two mechanistic manifolds (metallacyclopentane intermediacy or direct carbometallation). Rather, these processes take place via a Ni-Ti-allyl complex. 

In the Zr-calalyzed enantioselective alkylation reactions discussed above, we discussed transformations that involve the addition of alkylmag-nesium halides and alkylaluminum reagents to olefins. With the exception of studies carried out by Negishi and co-workers, all other processes... 

Toxicity Trimethylaluminum and related alkylaluminum reagents are pyrophoric materials that can react explosively with the moisture in tissues, causing severe bums. The heat of reaction can also ignite the methane gas generated, resulting in thermal bums. Alkylaluminum reagents are corrosive substances, and contact is extremely destractive to the eyes, skin, and mucous membranes. Inhalation of trimethylaluminum and other volatile alkylaluminum compounds may cause severe damage to the respiratory tract and can lead to fatal pulmonary edema. 

A timeline for the development of olefin metathesis, adapted from a review by Grubbs, is shown in Figure 21.3. Olefin metathesis is more than 50 years old. " It was first conducted with ill-defined rhenium, molybdenum, and tungsten systems generated from perrhenate, aluminum oxide, - and tetraethyl lead as additive, from molybdenum oxide on p-TiO and tetramethyltin as additive, ° or from tungsten phenoxides supported on niobium oxide and silicon oxide activated with alkylaluminum reagents. The temperatures for these processes are hi, but the catalysts are relatively inexpensive and can be long lived. These are the types of catalysts that have been used for the synthesis of commodity chemicals by olefin metathesis. 

---