Epimerization in the NaBH4 reduction of asymmetric ketones

Hach, V.; Fryberg, E. C.; McDonald, E B

doi:10.1016/s0040-4039(01)96936-9

Cited by 10 publications

(8 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…When the reaction was performed with 8, in which the 1-0-mesyl group (of 2) is replaced by 0-(methoxy)trityl, the outcome was wholly different: an olefin was formed through the removal of a primary (H-6) rather than a secondary (H-4) proton, and nucleophilic displacement also took place. Results similar to those for 8 were obtained with the 2-epimer of 2, i.e., 2,3,4,6-tetra-O-benzyl-1,5-di-O-mesyl-~-rnannitol (12). It is suggested that selective displacement of the 1-0-mesyl group of 2 by superoxide generates a 1-peroxy anion (6) that abstracts H-4 intramolecularly, promoting concomitant loss of the 5-mesyloxy group.…”

supporting

confidence: 74%

“…That is, in the reaction of 2,3,4,6-tetra-0-benzyl-l,5-di-0-mesyl-D-mannitol (12) with potassium superoxide, a mixture of displacement and elimination products was formed comparable to that described for the 0-mesyl-0-(methoxy)trityl derivative (8), and there was no indication whatever that an en01 ether corresponding to 4 had been produced. Hence, the 'H nmr spectrum of the peracetylated reaction mixture, which showed that the 0-mesyl substituents had been completely removed, contained a prominent doublet (6 6.42, JlY2 = 13.0 Hz) commensurate with a 1-hexenitol structure (13) analogous to 11.…”

Section: Introductionmentioning

confidence: 86%

“…The syrupy residue (12.1 g) was treated with methanesulfonyl chloride as described above (12) 2,3,4,6-Tetra-0-benzyl-D-mannopyranose8 was reduced with sodium borohydride in aqueous tetrahydrofuran, as described above under 18, and then methanesulfonated, as described under 2. For personal use only.…”

Section: -0-mesyl-i-0-(methoxy)trityl-2346-tetra-mentioning

confidence: 99%

See 2 more Smart Citations

Regioselective eliminations in reactions of carbohydrate derivatives with superoxide, or with borohydride in 2-propanol

Rao¹,

Perlin²

1981

Can. J. Chem.

View full text Add to dashboard Cite

Thispaper is dedicated to Prof. Raymond U . Lemieux on the occasion of his 60th birthday VANGA S. RAo and ARTHUR S. PERLIN. Can. J. Chem. 59,333 (1981).The reaction between 2,3,4,6-tetra-0-benzyl-1,5-di-O-mesyl-~-glucitol(2) and potassium superoxide resulted in the loss of H-4 and the 5-mesyloxy (as well as 1-mesyloxy) substituent, and an almost quantitative conversion into en01 ether 4, i.e., 1,3,4,5-tetra-O-benzyl-3-dehydro-2-deoxy-~-threo-hex-2-enitol. When the reaction was performed with 8, in which the 1-0-mesyl group (of 2) is replaced by 0-(methoxy)trityl, the outcome was wholly different: an olefin was formed through the removal of a primary (H-6) rather than a secondary (H-4) proton, and nucleophilic displacement also took place. Results similar to those for 8 were obtained with the 2-epimer of 2, i.e., 2,3,4,6-tetra-O-benzyl-1,5-di-O-mesyl-~-rnannitol (12). It is suggested that selective displacement of the 1-0-mesyl group of 2 by superoxide generates a 1-peroxy anion (6) that abstracts H-4 intramolecularly, promoting concomitant loss of the 5-mesyloxy group. The transition state for proton abstraction within anion 6 appears to be more stable than that of the corresponding anion in the manno series, accounting for the different reaction routes for 2 and 12. Elimination occurred also in the reduction of 2,3,4,6-tetra-0-benzyl-D-glucopyranose with sodium borohydride in 2-propanol, en route to 2, affording 2,4,6-tri-0-benzyl-2-dehydro-3-deoxy-~-threo-hex-2-enitol (21). The 'H nmr spectra of alditol derivatives 2, 8, and 12 show that these molecules depart substantially from extended zigzag conformations, in contrast to configurationally related peracetylated acyclic derivatives. 1,3,4,5 dehydro-3 deoxy-2 L-thrio-hexbne-2 itol. Si I'on effectue la meme reaction sur le compose 8qui correspond au remplacement du groupe 0-mesyl-1 (de 2) par un groupe 0-(methoxy)trityl, la reaction est tres differente. I1 se forme une olefine par I'intermediaire d'une elimination de I'hydrogeneprirnaire (H-6) plutBt que parcelle du proton (H-4) et il se produit ainsi un deplacement nucleophile. IAvec I'Cpimkre du compose 2, soit le tetra-0-benzyl-2,3,4,6 di-0-m6syl-1,5 D-mannitol (l2), on obtient des resultats semblables a I ceux que donne le compose 8. On suggere que le d6placement selectif du groupe 0-mesyl-1 du compos6 2 par le superoxyde, engendre un anion peroxy (6) qui enleve intramoleculairement H-4 en favorisant la perte concomitante du groupe mesyloxy en position 5. L'etat de transition lors de l'elimination du proton dans I'anion (6) semble itre plus stable que celui derivant de I'anion correspondant des series manno; ceci explique les reactions differentes de 2 et 12. Lors de la reduction du tetra-0-benzyl-2,3,4,6 D-gl~copyI'ano~e par le borohydrure de sodium dans le propanol-2, il se produit egalement une elimination qui conduit au tri-0-benzyl-2,4,6dChydro-2deoxy-3 D-thrio-hexene-2 it01 (21) plutBt qu'au compose 2 attendu. Les spectres rmn du 'H des derives alditol2,8, et 12 indiquent que ces molCcules s'eloignen...

show abstract

supporting

confidence: 74%

Section: Introductionmentioning

confidence: 86%

See 1 more Smart Citation

Regioselective eliminations in reactions of carbohydrate derivatives with superoxide, or with borohydride in 2-propanol

Rao¹,

Perlin²

1981

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…(3) a-OH (4) a-OH (5) a-OH (6) a-OH (7) a-OAc (8) a-OH (10) a-OH (11) a-OAc (13) a-OBz (14) a-OBz (15) a-OBz (16) a-OBz Dreoonderance of the ketol or the dio-…”

Section: R1unclassified

“…Bromination of the dihydroketol acetate (11) gave a crystalline monobromide (12) in good yield. The n.m.r.…”

Section: R1mentioning

confidence: 99%

Beyerane diterpenes: structure and reactivity of the α-ketol ent-3β-hydroxybeyer-15-ene-2,12-dione, its corresponding diosphenol, and synthesis of the isomeric α-ketol acetates

Piacenza¹,

Pegel²,

Phillips³

et al. 1979

J. Chem. Soc., Perkin Trans. 1

View full text Add to dashboard Cite

show abstract

ChemInform Abstract: EPIMERISIERUNG BEI DER RED. ASYMMETRISCHER KETONE DURCH NATRIUMBORHYDRID

Hach¹,

Fryberg²,

McDonald³

1971

Chemischer Informationsdienst. Organische Chemie

View full text Add to dashboard Cite

show abstract

Epimerization in the NaBH4 reduction of asymmetric ketones

Cited by 10 publications

References 3 publications

Regioselective eliminations in reactions of carbohydrate derivatives with superoxide, or with borohydride in 2-propanol

Regioselective eliminations in reactions of carbohydrate derivatives with superoxide, or with borohydride in 2-propanol

Beyerane diterpenes: structure and reactivity of the α-ketol ent-3β-hydroxybeyer-15-ene-2,12-dione, its corresponding diosphenol, and synthesis of the isomeric α-ketol acetates

ChemInform Abstract: EPIMERISIERUNG BEI DER RED. ASYMMETRISCHER KETONE DURCH NATRIUMBORHYDRID

Contact Info

Product

Resources

About