Anhydrides asymmetric reductions

Synthesis of left-hand segment began with 7-benzyloxyindole 197. A Vilsmeier-Haack formylation followed by condensation afforded nitroalkene 198. Reduction, acylation with succinic anhydride, and subsequent Bischler-Napieralski cyclization provided dihydro-p-carboline 199. Noyori asymmetric reduction of 199, further treatment with A-iodosuccinimide, followed by activation with silver triflate in the presence of dimethoxy-N,N-diallylaniline furnished the desired coupling product 200. Subsequent saponification and cyclization via a ketene intermediate gave the rearrangement precursor 201. Oxidative skeletal rearrangement initiated by m-CPBA followed by removal of the Fmoc group and conversion of the aniline to the hydrazine furnished Fischer indole precursor 202 (Scheme 35). 

Asymmetric hydrogenation offers a useful synthetic route to chiral amines. Although the mechanism is unknown, only the (7%/V-acetyl-1 -arvlalkylamine 21 with 95% ee was obtained by the hydrogenation of a mixture of ( )- and (Z)-enamides 20a and 20b using Rh-Me-DuPHOS (XI). The A-acetvl enamines 20a,b are prepared by the reduction of oximes with Fe powder in acetic anhydride [21]. Also the acetamide 23 was obtained from 22 [22]. 

Intramolecular asymmetric induction has also been used in electrochemistry as in the reduction of optically active alcohol esters or amides of a-keto [469,470] and unsaturated [471] acids and oximes [472] and in the oxidation of olefins [473]. A maximum asymmetric yield of 81% was obtained in the reduction of (5 )-4-isopropyl-2-oxazolidinone phenyl-glyoxylate [470]. Nonaka and coworkers [474,475] found that amino acid A-carboxy anhydrides were polymerized with various electrogenerated bases as catalyst to give the poly(amino acids) with high chirality in high yields. Conductive chiral poly(thiophenes) prepared by electropolymerization can be used for chiral anion recognition [476]. 

Both (R)-(-t-)- and (S)-(-)-tertiarybutylphenylphosphine sulphides (6) have been synthesised in high optical purity from (S)-(-)- and (R)-(+)-tertiarybutylphosphinothioic acids, respectively, by formation of the mixed anhydride (5) followed by borohydride reduction (Scheme 2). Reactions of the product (6) have been used to provide routes to optically active phosphinothioic iodides, phosphinodithioates and thioselenophosphinic acids of known configurations. A new method for the asymmetric synthesis of tertiary phosphine oxides has been reported.5 An Arbusov reaction of the optically active 1,3,2-... 

Freskos reported the synthesis of chiral succinate using Pd-catalyzed carbonylation of enol triflate 26 (Scheme 18) followed by asymmetric hydrogenation of resulting a,/3-unsaturated ester 27 using a ruthenium complex. - " In the absence of HCOOH, the yield was low (15-20%). Similarly, when water was substituted for formic acid, low product yields (15-20%) were observed. As one possible pathway to produce 27, reductive elimination from the palladium complex to yield a mixed anhydride derived from the product and triflic acid would be considered. 

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