Asymmetric syntheses via chiral organoboranes based on α-pinene

Brown, Herbert C.; Ramachandran, Prakash

doi:10.1016/s1874-5148(06)80007-2

Cited by 26 publications

(13 citation statements)

References 201 publications

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“…Enantiofacial Selectivity in the Hydroboration of Alkenes with IpcBH 2 . The importance of (R-pinene)derived borane reagents in synthesis 23 prompted us to examine the asymmetric hydroboration of prochiral alkenes with IpcBH 2 through our 11 B NMR technique. The hydroboration process results in the formation of diastereomeric mixed dialkylborane intermediates from both trans and trisubstituted olefins.…”

Section: Resultsmentioning

confidence: 99%

New Direct ¹¹B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides

et al. 2003

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Representative organoborane mixtures were quantitatively converted to their borohydrides through their reaction with activated KH (KH), permitting their detailed analysis by (11)B NMR. Through the treatment of commercial KH with a THF solution of lithium aluminum hydride (LAH), a dramatic change in the surface morphology results as revealed by scanning electron microscopy (SEM). Energy dispersed spectroscopy (EDS) was employed to reveal that the LAH treatment deposits a significant amount of an unknown aluminum-containing species on the surface of the KH, which imparts a unique reactivity to the KH. Even highly hindered organoboranes are quantitatively converted to their borohydrides by replacing electronegative groups (e.g., OR, halogen) with hydrogen, retaining only the carbon ligation. Through this simple KH treatment, complex organoborane reaction mixtures are converted to the corresponding borohydrides whose (11)B NMR spectra normally exhibit resolved signals for the individual species present. The integration of these signals provides quantitative information on the relative amounts of each component of the mixture. New generalities for the effect of alpha-, beta-, and gamma-substituents have also been determined that provide a new, simple technique for the determination of the isomeric distribution in organoborane mixtures resulting from common organoborane processes (e.g., hydroboration). Moreover, the (1)H-coupled (11)B NMR spectra of these mixtures reveal the extent of alkylation for each species present. Representative organoboranes were examined by this new technique permitting a simple and convenient quantitative analysis of the regio- and diastereomeric composition of a variety of asymmetric organoborane processes. Previously unknown details of pinene-based hydroborations and reductions are revealed for the first time employing the KH (11)B NMR technique.

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Section: Resultsmentioning

confidence: 99%

New Direct ¹¹B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides

et al. 2003

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“…Semiempirical calculations were carried out using the AM1 method 4 as outlined in the Computational Details section. The four borane reagents, i.e., Ipc 2 BCl, Eap 2 BCl, B- t- BuIpcBCl, and B- t- BuEapBCl, were all derived from (+)-α-pinene. 3b-e…”

Section: Resultsmentioning

confidence: 99%

“…According to the AM1 semiempirical calculations published previously, 1a,b in the reductions of benzaldehyde - 1 -d and acetophenone3a with boranes based on (+)-α-pinene, 3b-e the stereoselectivity is mainly imposed by the different energy requirements of the competing B-sp 2 → B-sp 3 rather than of the C-sp 2 → C-sp 3 coordination expansion processes, i.e., during formation of the boron−oxygen bond in the initial diastereomeric charge-dipole complexesCD intermediatesrather than during formation of the diastereomeric carbon−hydrogen bonds in the conversion of the charge-dipole intermediates into the corresponding transition-states.…”

Section: Introductionmentioning

confidence: 99%

How Borane Reagents Based on α-Pinene Control Stereoselectivity in the Reductions of Carbonyl Groups with Different Stereogenic Elements. 3. The Effect of the Relative Size and Conformation of the Carbonyl Substituents on the Stereoselectivity of the Ipc₂BCl, Eap₂BCl, B-t-Bu-IpcBCl, and B-t-Bu-EapBCl Reagents. A Semiempirical Study

Rogić¹

2000

J. Org. Chem.

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The reductions of a more elaborate prostereogenic nonchiral and chiral ketones with the representative borane reagents derived from (+)-alpha-pinene confirm that the overall stereoselectivity, similarly to the previously studied reductions of benzaldehyde and acetophenone, is also controlled, early along the reaction coordinate, by the structure of the borane reagent. The stereoselectivity reflects the energy differences among syn-1, 3-interactions of the smallest of the three boron substituents in the reacting borane conformation with the two carbonyl substituents in the substrate. For the B-alkyl-IpcBCl reagents and the R(S)-CO-R(L) substrates, these are the interactions of the B-Cl with the C-R(S) and C-R(L) bonds. To minimize developing intermolecular syn-1,3-interactions with the reagent's B-Cl bond during the reaction, in the conformationally mobile R(S)-CO-R(L) systems, the R(L) and R(S) groups seek to adopt a more reactive conformation even at the expense of the unfavorable intramolecular interactions.

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“…464 All four possible diastereoisomeric NADH model compounds 308 have been synthesised and characterised, and one of them reduces methyl phenylglyoxylate to give methyl (S)-(+)-mandelate of 72% ee. 465 The applications of chiral pinene-derived organoboranes in asymmetric synthesis have been reviewed, 466,467 as have recent advances in the utilisation of B-chlorodiisopinocampheylborane (DIP-Cl) 309. 468 A convenient and economical preparation of 309 from -pinene 239 by reaction with NaBH 4 -BCl 3 in 1,2-dimethoxyethane has been described, 469 as have generally applicable syntheses of various [monoterpene] 2 BX derivatives where X is Cl, Br or I.…”

Section: Pinanesmentioning

confidence: 99%

Monoterpenoids

Grayson¹

1998

Nat. Prod. Rep.

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Species Principal constituents ReferenceAbies balsamea Mill -and -pinene, -phellandrene, limonene Achillea biebersteinii Afan piperitone, or cineol and camphor Aloysia triphylla (L'Herit.) Britton citral, limonene Alpinia conchigera Griff. cineol Alseuosmia macrophylla A. Cunn. flowers: linalool Ambrosia microcephala DC. camphor, bornyl acetate Amomum subulatum Roxb. cineol, -terpineol, -and -pinene Artemisia afra yomogi alcohol, artemisyl acetate Artemisia afra Willd. cineol, terpinen-4-ol, borneol Artemisia ordosica -and -pinene, sabinene Austromyrtus dulcis (C. T. White) L. S. Smith (chemotype) -pinene, cineol Boronia megastigma Nees. -ionone, 8-hydroxylinalyl esters, geranyloxy cinnamate Bouea macrophylla Griff. ( E)--ocimene, -pinene Calamintha cretica piperitenone, piperitenone oxide Calamintha incana (Sm.) Boiss. piperitenone oxide Callistemon speciosus Anthor. cineol, -pinene, -terpineol Canella winteriana Gaertn. stem and bark: cineol, terpinen-4-ol, -terpinyl acetate, -terpineol; leaves: myrcene Cedronella canariensis Webb et Berth. ssp. canariensis pinocarvone Chamelaucium uncinatum genotypes -pinene, citronellal, limonene, linalool, -terpinyl acetate Chenopodium ambrosioides limonene, trans-pinocarveol Chenopodium botrys -8 Chrysanthemum balsamata carvone, camphor Chrysanthemum lavandulaefolium menthol Cinnamomum camphora Nees et Ebermaier camphor, cineol, terpinen-4-ol, limonene Cinnamomum puciflorum -2 Citrus grandis limonene Clausena anisata (Willd.) J. D. Hook limonene, myrcene Coleus aromaticus carvacrol, camphor Coreopsis barteri Oliv. & Hiern limonene, -phellandrene Coreopsis grandis Hogg ex Sweet myrcene Coriandrum sativum seeds: linalool Coridothymus capitatus Reich. f. carvacrol 98, 99 Cunila fasiculata menthofuran Cunila microcephala menthofuran, limonene Curcuma aeruginosa Roxb. cineol, camphor Curcuma amada Roxb. myrcene Curcuma aromatica Salisb. cineol, camphor, isoborneol, camphene Curcuma cochinchinensis Gagnep. cineol Curcuma domestica -phellandrene, cineol, p-cymene, -pinene Curcuma pierreana Gagnep. Rhizome, stem: isoborneol, isobornyl acetate leaf: isoborneol, camphor Croton aubrevillei J. Leonard linalool Croton zambesicus Muell. Arg. linalool Cyclotrichum origanifolium (Labill.) Manden. et Scheng. cis-isopulegone, pulegone, isomenthone, menthol Cymbopogon caesius (Nees et Hook. et Arn.) Stapf. perillyl alcohol, geraniol, limonene Cymbopogon citratus (DC.) Stapf. citral, geraniol, myrcene, -and -pinene Cymbopogon khasianus (Munro ex Hack.) Bor. geraniol, geranyl acetate, linalool Cymbopogon schoenanthus piperitone, limonene Daphne mezereum flowers: linalool, linalyl oxides Echinophora chryantha Freyn et Sint. -phellandrene Egletes viscosa various terpenol acetates Elsholtzia ciliata (Thunb.) Hyland chemotype (a): elsholtzia ketone, -thujone chemotype (b): neral, geranial, limonene

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Asymmetric syntheses via chiral organoboranes based on α-pinene

Cited by 26 publications

References 201 publications

New Direct ¹¹B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides

New Direct ¹¹B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides

Monoterpenoids

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Asymmetric syntheses via chiral organoboranes based on α-pinene

Cited by 26 publications

References 201 publications

New Direct 11B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides

New Direct 11B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides

Monoterpenoids

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New Direct ¹¹B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides

New Direct ¹¹B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides