Lithium aluminum hydride enantioselective synthesis

In this context, a chiral hydride reagent, BINAL-H, prepared by modification of lithium aluminum hydride with equimolar amounts of optically pure binaphthol and a simple alcohol, is extremely useful (9b, 18a, 35) Scheme 15 shows the utility of the three-component coupling synthesis. The < > side-chain unit and the hydroxycyclopentenone can be prepared with very high enantioselectivity by reduction of the corresponding enone precursors (35-38). 

Cycloadditiom. This reaction provides an enantioselective synthesis of a cyclooctane-containing terpenoid (5). The optically active precursor (3) was obtained by reduction of the r-alkyl alkynyl ketone 1 with lithium aluminum hydride... 

The enantioselective reduction of unsymmetrical ketones to produce optically active secondary alcohols has been one of the most vibrant topics in organic synthesis.8 Perhaps Tatchell et al. were first (in 1964) to employ lithium aluminum hydride to achieve the asymmetric reduction of ketones9 (Scheme 4.IV). When pinacolone and acetophenone were treated with the chiral lithium alkoxyaluminum hydride reagent 3, generated from 1.2 equivalents of 1,2-0-cyclohexylidene-D-glucofuranose and 1 equivalent of LiAlHzt, the alcohol 4 was obtained in 5 and 14% ee, respectively. Tatchell improved the enantios-electivity in the reduction of acetophenone to 70% ee with an ethanol-modified lithium aluminum hydride-sugar complex.10... 

Oppolzer has developed a method of asymmetric synthesis based on the use of the chiral auxiliaries 39A and 39B derived respectively from (+ )-camphor [(+ )-40] and (- )-camphor [(- )-40]. Crotonylation of 39A gave the ester that was attacked by 4-methyl-3-pentenyllithium in the presence of copper iodide tributylphosphine and boron trifluoride from only one side of the molecule, the product 41 having the (S)-configuration (enantioselectivity 98.5%). The ester 42—similarly obtainable from 39B—was methylated under similar conditions, also yielding 41 with 92% enantioselectivity. (S)-Citronellic acid [(S)-36] or (S)-citronellol [(S)-33] were then obtained from 41 by the action of sodium hydroxide or lithium aluminum hydride (Scheme 6). Reduction of potassium... 

S,S)-2,3-Butanediol (see Section 4.1.2. for access to this compound) was the starting material for the synthesis of (S,S)-2,3-dimethyl-18-ciown-6 (6) which has been used as a chiral catalyst in the enantioselective Michael addition reaction (Sections D.1.5.2.1. and D.I.5.2.4.). Chain elongation of the diol by reaction with ethyl diazoacetate and lithium aluminum hydride reduction, followed by cyclization with triethyleneglycol ditosylate, gives the crown ether 610. 

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