Organoaluminum-promoted rearrangement

For further examples of regioselective rearrangements with organoaluminum reagents see refs 123 and 129. For organoaluminum-promoted rearrangements of allylphenyl ethers see ref 140. 

Maruoka K, Ooi T, Yamamoto H. Organoaluminum-promoted rearrangement of epoxy silyl ethers to p-siloxy aldehydes. J. Am. Chem. Soc. 1989 111 6431-6432. 

Organoaluminum-promoted Beckmann rearrangement/methylation of cyclohexanone oxime mesylate, followed by allylation of ketimine 40a and Mannich cyclization of the intermediate iminium-allylsilane, provides piperidine 40b possessing cxo-unsaturation (08BKC1669). 

The organoaluminum-promoted Claisen rearrangement139 of allyl vinyl ethers such as (f )-( )-6-methyl-4-vinyloxy-2-heptenc leads preferentially to Ry(E)- or (S)-(Z)-1 depending on the reagent employed 14°. The rearrangement products have been assigned by correlation (see p 437). i... 

Treatment of a wide variety of oxime sulfonates with several equivalents of alkyl-aluminum reagents in CH2CI2 resulted in formation of the imines, which were directly reduced with excess DIBAH to give the corresponding amines, as shown in Sch. 19. This organoaluminum-promoted Beckmann Rearrangement of oxime sulfonates has been successfully applied to the stereoselective synthesis of naturally occurring alkaloids, pumiliotoxin C, and solenopsin A and B, as illustrated in Sch. 20 [43]. 

Combination of silyl enol ethers with the organoaluminum-promoted Beckmann rearrangement of oxime sulfonates resulted in a novel reaction system that leads to the formation of enaminones [44]. Treatment of a mixture of anfr-2-methylcyclohexa-none oxime sulfonate (33) and 2-(trimethylsiloxy)-l-octene in dry CH2CI2 with Et2AlCl at -78 °C for 30 min, and at 20 °C for additional 1 h resulted in formation of the enaminone 34 in 90 % yield (Sch. 21). 

Gephyrotoxin (106), a constituent of the skin extraas of the poison-dart hrog, was synthesized as outlined in Scheme 11. The organoaluminum-promoted Beckmann rearrangement produced an imine, which was stereoselectively reduced (essentially total selectivity) with DIBAL to a ord piperidine (109 41% yield). 

N.S. Mani and co-workers utilized the organoaluminum promoted modified Beckmann rearrangement during their efficient synthetic route to chiral 4-alkyl-1,2,3,4-tetrahydroquinoline. (4R)-4-Ethyl-1,2,3,4-tetrahydroquinoline was obtained by rearrangement of the ketoxime sulfonate of (3R)-3-ethylindan-1-one. The resulting six-membered lactam product was reduced to the corresponding cyclic secondary amine with diisobutylaluminum hydride. 

The salient feature of the synthesis is the organoaluminum-promoted stereospecific pinacol-type 1,2-rearrangement common to both segments. The 338—>339 rearrangement (Scheme 46) proceeds with preservation of alkene geometry, and is completely enantiospecific. The other 1,2-rearrangement, 345 —> 346 (Scheme 47), also proceeds with no EjZ isomerization of the olefin and with complete enantiospecificity. 

Recently, Maruoka reported a new chiral bimetallic organoaluminum reagent 10 for asymmetric Claisen rearrangement (Scheme 2.3) [9]. This reagent activates the allyl vinyl ether to promote rearrangement with double coordination to oxygen. 

Nonoshita K, Banno H, Maruoka K, Yamamoto H (1990) Organoaluminum-promoted Claisen rearrangement of allyl vinyl ethers. J Am Chem Soc 112 316... 

Another synthetic route via the Beckmann rearrangement, which is promoted by organoaluminum reagent along with alkylation, involves a new stereoselective reduction of the imino group. The starting oxime sulfonate (228) was synthesized from cyclopentanone (226) in three steps Reaction of 226 with 1-undecene in the presence of silver oxide produced the a-undecylcyclopentanone (227) which on successive treatment with hydroxylamine and methanesulfonyl chlo-ride-triethylamine gave the mesylate (228). Treatment of the oxime mesylate... 

TableS. Claisen Rearrangements Promoted by Bulky Organoaluminum Reagents123...

Abstract The use of organoaluminum-based Lewis acids (A1R X3 R = alkyl, alkynyl, X = halide or pseudohalide) in the period 2000 to mid-2011 is overviewed with a focus on (1) stoichiometric reactions in which one of the organoaluminum substituents is transferred to the substrate (e.g., the opening of epoxides, 1,2-additions to carbonyl compounds, coupling with C-X, and Reissert chemistry) and (2) asymmetric, often catalytic, reactions promoted by Lewis acid catalysts derived from organoaluminum species (e.g., use of auxiliaries with alanes, Diels-Alder, and related cycloaddition reactions, additions to aldehydes and ketones, and skeletal rearrangement reactions). 

As an example of asymmetric intermolecular sigmatropic rearrangement, chiral Lewis acid promoted carbonyl-ene reactions have been utilized as the powerful tool for stereocontrolled carbon-carbon bond formation processes. In 2004, Mamoka et al. demonstrated enantioselective hetero-carbonyl-ene reaction of aldehydes and 2-methoxypropene catalyzed by chiral organoaluminum complex 64, giving enantiomerically enriched (3-hydroxymethylketones (Scheme 45) [78]. 

---