Acetates organoaluminums

Various carbon nucleophiles, such as allylsilanes, allylstannanes, silyl enol ethers, ketene silyl acetals, organoaluminum compounds, and Grignard reagents were effective as carbon nucleophiles. 

Dialkylvinylaluminums transfer their vinyl substituent to stereodefined allylic acetates with Pd° catalysis with overall inversion of configuration. Metal attack of the organoaluminum is thereby indicated (equation 173).154... 

In later communications (27, 28) Hirooka reported that in addition to acrylonitrile, other conjugated monomers such as methyl acrylate and methyl methacrylate formed active complexes with organoaluminum halides, and the latter yielded high molecular weight 1 1 alternating copolymers with styrene and ethylene. However, an unconjugated monomer such as vinyl acetate failed to copolymerize with olefins by this technique. 

Kita, Fujioka and co-workers reported that the reaction of a-alkoxycycloalkanone oxime acetates sueh as 35 with organoaluminum reagents caused Beckmann fragmentation and subsequent carbon-carbon bond formation to give different (o-eyano-a-alkyl (or alkynyl) ethers of type 36 in high yield, as illustrated in Sch. 22 [45]. 

Yamamoto and Maruoka investigated the reaction of chiral acetals with organoaluminum reagents. Unprecedented regio- and stereochemical control was observed in the addition of trialkylaluminums to chiral a,/3-unsaturated acetals derived from optically pure tartaric acid diamide [83]. The course of the reaction seemed to be highly influenced by the nature of substrates, solvents, and temperature. These findings provide easy access to optically active a-substituted aldehydes (84), /3-substituted aldehydes (85), a-substituted carboxylic acids (86), or allylic alcohols (87). Because optically pure RJi)- and (5,5)-tartaric acid diamides are both readily available, this method enables the predictable synthesis of both enantiomers of substituted aldehydes, carboxylic acids, and allylic alcohols from a,/3-unsaturated aldehydes (Sch. 54). 

Kinetic resolution of chiral acetals has been effected by use of some organoaluminum reagents [84], On treating a chiral acetal 88, derived from (2, 4/ )-(-)-pentanediol, with -Bu3A1 at room temperature, one diastereomer was found to react much faster than the other, and the residu enol ether is transformed into optically pure ketone. The efficiency of this method is demonstrated by a concise synthesis of (5)-(-)-5-hexadecan-l,5-lactone (89), the pheromone of Vespa orientalis, as shown in Sch. 56. 

This reaction has been further extended to the asymmetrization of the symmetric acetal, and to different modified organoaluminum reagents including i-BuaAl and bulky organoaluminum amides (Sch. 57) [85],... 

The final example of 1,2-additions of organoaluminums to masked ketone substrates is outlined in equation (15). The addition of a large excess (10 equiv.) of trimethylaluminum to a variety of triol acetals and ketals proceeds in relatively high overall yield. Although ketal substrates where R did not equal were not attempted, a number of acetals were prepared and upon exposure to MesAl they afforded the corresponding diastereomeric ethers with poor diastereoselectivity (33-17% de). 

This type of reaction attracted broad interest when it was discovered that high regioselectivity can also be effected with organoaluminum compounds and other nucleophiles in the presence of Lewis acids and that by employing chiral cyclic acetals (from optically active 1,2- or 1,3-diols) diastereoselective transformations can be realized. - Such reactions are synthetically very valuable when considering that the overall process represents an enantioselective Michael addition, where the chiral auxiliary can be recycled (Scheme 39). ... 

Reduction of cyclic acetals and orthoethers with organoaluminum reagents 02MI17. 

Further studies indicated that aluminum alkyls are capable of capturing an oxo-nium intermediate generated from the corresponding acetal (Scheme 6.155) [199]. The substrate 160, in which a hydroxy group was substituted by acetal, was amenable to this type of rearrangement and subsequent alkylation by alkylaluminum species. Again the dual function of organoaluminum as a Lewis acid and a base were demonstrated. 

The reaction between alkyl halides and aluminum metal is the basis of the oldest method for the synthesis of organoaluminum compounds. For example, propargylic bromides react with aluminum in ether giving organoaluminum compounds that on treatment with acetals yield solely a-allenic ethers (equation 1)." However, the reaction of simple alkyl halides with aluminum metal requires a long reaction time. 

The addition of Lewis acids also irr iroves the yield for a Beckmann fragmentation followed by carbon-carbon bond formation through reaction of oxime acetates with organoaluminum reagents (eq 115). ZnCL is generally more effective than TMSOTf for this transformation. ... 

It was reported that it is possible to employ persistent phosphorus-based radicals in controUed/Uving free-radical polymerization [283, 284]. Also, in cases of low stability of the hyper coordinated radicals, the ligand exchanges become facile and some organoaluminum, organoboron, and other compounds have been used successfully as transfer agents in polymerizatimi of styrene, acrylics, and vinyl acetate [283, 284]. 

---