A Modified Method for the Meerwein-Ponndorf-Verley Reduction

Truett, W. L.; Moulton, Wilbur N.

doi:10.1021/ja01156a558

Cited by 11 publications

(3 citation statements)

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“…The supernatant liquid is decanted, filtered through Celite, washed with water, dried over MgSO 4 , and concentrated in vacuo to a colorless, crystalline residue (3.4 g), which is shown by NMR to consist mainly of a mixture of meso - and rac -( E , E )-1 (58:42), and some 1,3-diphenylpropene (vide infra). Acidification of the aqueous extract and extraction with ether gives 0.6 g crude α-phenylcinnamic acid: mp 171−172 °C (lit . mp 173 °C) after recrystallization from heptane.…”

Section: Methodsmentioning

confidence: 99%

A Non-Cope among the Cope Rearrangements of 1,3,4,6-Tetraphenylhexa-1,5-dienes

et al. 1999

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The set of 1,3,4,6-tetraphenylhexa-1,5-dienes (1) represents a perturbation of Cope's rearrangement by four radical-stabilizing phenyl groups all positioned to drive the transition region toward the homolytic−colligative end of the mechanistic spectrum. The appearance of (Z)-isomers being suppressed thermodynamically by a steric interaction of +2.6 kcal mol-1 per cis double bond, an equilibration that is stereochemically not of any Cope type, emerges as the predominant reaction. It is an interconversion of rac -( E , E )-1 and meso -( E , E )-1 (48:52; 77.3−115.3 °C) with the following values of the enthalpy, entropy, and volume of activation: ΔH ⧧ = 30.7 ± 0.2 kcal mol-1, ΔS ⧧ = +2.1 ± 0.4 cal mol-1 K-1, and ΔV ⧧ = +13.5 ± 0.1 cm-3 mol-1, respectively. Structures have been established by X-ray crystallographic analysis; a possible relationship between dihedral angle and bond lengths in the styrene portions is proposed. The entropy of activation is incompatible with a chair or boat Cope rearrangement; the volume of activation is neither low enough for a pericyclic Cope (“concerted”) mechanism nor high enough for a homolytic−colligative mechanism involving full dissociation as the rate-determining step. Trapping and a crossover experiment give some but only partial support to the intermediacy of free radicals. At higher temperatures, however, electron spin resonance experiments demonstrate an equilibrium with kinetically free (E,E)-1,3-diphenylallyl radicals. These observations are rationalized in terms of geometric reorganization within the confines of a ‘cage'. Resolution by chiral chromatography of rac -( E , E )-1 allows recognition of a fast racemization (40−65 °C), of which ΔH ⧧ (21.3 ± 0.1 kcal mol-1), ΔS ⧧ (−13.2 ± 0.3 cal mol-1 K-1), and ΔV ⧧ (−7.4 ± 0.4 cm-3 mol-1) are consistent with a pericyclic Cope rearrangement. Enriched (Z)-isomers undergo Cope rearrangements in accord with the known influence of axiality and the chair/boat alternative on the energy of the transition region.

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Section: Methodsmentioning

confidence: 99%

A Non-Cope among the Cope Rearrangements of 1,3,4,6-Tetraphenylhexa-1,5-dienes

et al. 1999

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“…l-Phenvlethanol-/-d, which was obtained by reduction of acetophenone with lithium aluminum deuteride, was identical in properties with those reported.30 Benzhydrol-7-d, obtained by reduction of purified benzophenone with lithium aluminum deuteride, possessed properties identical in all respects with those listed in the literature. 31 Kinetic Methods. Cary Model 16.…”

Section: Methodsmentioning

confidence: 99%

Electron bridges in the mechanisms of chromic acid oxidation of alcohols

Kwart¹,

Nickle²

1976

J. Am. Chem. Soc.

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ethane, as evidenced by the admixture of the corresponding authentic samples. The major pyrolysis product acetyl chloride (5) was further identified by hydrolysis and concurrent formation of additional acetic acid (7); chloroform and 1,1,2,2-tetrachloroethane were also identified by GLC analysis.Model Experiments Concerning the Mode of Formation of Acetyl 1,l-Dichloroethyl Peroxide (12) and Diacetyl Peroxide (13). (a) Attempted Reaction of 1,4-Dimethyl-1,4-dichloro-2,3,5,6-tetroxolane (9) with Acetyl Chloride. A solution of 40 mg (0.21 mmol) of 9 and 35 mg (0.45 mmol) of acetyl chloride in 1 g of dichloromethane was kept at ambient temperatures for 2 days and was then heated to 45 OC for 30 min. Neither 12 nor 13 could be detected by N M R analysis.(b) Attempted Conversion of 1,4-Dimethyl-1,4-dichloro-2,3,5,6tetroxolane (9) into Diacetyl Peroxide under Mild Conditions. To a solution of 40 mg of 9 in 2 ml of methyl acetate, 3 drops of water were added and the mixture was kept at room temperature for 1 day. N M R analysis showed that 9 was unchanged and no diacetyl peroxide (13) was formed. Acknowledgment. The authors wish to express their gratit u d e t o ProfessorAbstract: The solvatochromic comparison method is used to evaluate hydrogen-bonding contributions in HBD (hydrogen-bond donor) solvents to several commonly used dye indicator solvent polarity scales (Dimroth's E~o , Brooker's XR. Kosower's Z ) . Hydrogen-bonding effects on other spectral properties, equilibria, and reaction rates are determined, and the results are used to construct an a-scale of solvent HBD acidities.In part I of this series,2 information obtained through solvatochromic comparisons was used in constructing a p-scale + a a + b p (1) of solvent hydrogen-bond acceptor (tIBA)3 basicities. This p-scale was t o serve, together with a n a-scale of solvent hy-where a and b represent the susceptibilities of X Y Z to changing drogen-bond donor ( H B D I 3 acidities, toward correlation of solvent HBD3 acidity and H B A basicity, respectively. In t h e solvent effects on many reaction rates, equilibria, a n d spec-present paper we shall use the same solvatochromic comparison troscopic properties, X Y Z , through equations of t h e form method toward the formulation of the a-scale of solvent HBD X Y Z = X Y Z o + solvent polarity-polarizability effect Journal of the American Chemical Society / 98:lO / M a y 12, 1976

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“…Reduction of 8 (0.79 mmol) with NaBH 4 (2.64 mmol) was performed in 95% ethanol (2 mL) with stirring at room temperature for 30 min, after which the crude product was obtained following an aqueous workup (avg yield = 51%). Reduction of 8 with Al(O i Pr) 3 was achieved by adaptation of a known procedure: a mixture of 8 (0.39 mmol), aluminum isopropoxide (1.96 mmol), and anhydrous 2-propanol was refluxed for 45 min. After an aqueous workup, the product was extracted into CH 2 Cl 2 , dried, and rotary evaporated affording the crude product (avg yield = ∼100%).…”

Section: Methodsmentioning

confidence: 99%

Using NMR Spectroscopy and Chemical Synthesis to Establish Diastereoselectivity of NaBH₄ and Meerwein–Ponndorf–Verley (MPV) Reduction of (±)-Benzoin Isopropyl Ether: A Collaborative Discovery-Based Laboratory Experiment

et al. 2020

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A discovery-based undergraduate organic chemistry lab experiment has been developed in which students establish the diastereoselectivity of hydride reduction of the α-chiral ketone (±)-benzoin isopropyl ether to erythro and threo diastereomeric alcohols by two different reducing agents. Students achieve this goal by working collaboratively and using chemical, chromatographic (TLC), and NMR spectroscopic methods to identify the major diastereomers produced from each reduction. To this end, three groups of students perform three different reductions using three different reducing agents. Students in two groups carry out reduction of (±)-benzoin isopropyl ether: one uses NaBH 4 / ethanol, a widely used metal hydride reagent for reduction of aldehydes and ketones, and the other uses Al(O i Pr) 3 /2-propanol, a hydride transfer reagent used in the Meerwein−Ponndorf−Verley (MPV) reaction. Students in the third group use diisobutylaluminum hydride (DIBAL-H) to reductively ring-open meso-2,2-dimethyl-4,5-diphenyl-1,3-dioxolane (an acetal they synthesize in a previous experiment) to obtain an authentic sample of the erythro diastereomer unaccompanied by its threo counterpart. Students perform TLC analysis of NaBH 4 and MPV reaction products vs the authentic erythro sample to qualitatively establish the diastereoselectivity exhibited by NaBH 4 and MPV reduction of the ketone substrate. Afterward, students from all three groups share 1 H NMR spectra of their products and perform quantitative analysis by establishing the ratios of each diastereomer present using NMR integration values. Through experimentation, students learn how diastereomers can differ chromatographically and spectroscopically and yet not be readily distinguishable by such techniques. This experiment also serves as a pedagogically valuable complement to a previously described and highly popular discovery-based experiment that probes the diastereoselectivity in the NaBH 4 reduction of (±)-benzoin.

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A Modified Method for the Meerwein-Ponndorf-Verley Reduction

Cited by 11 publications

References 0 publications

A Non-Cope among the Cope Rearrangements of 1,3,4,6-Tetraphenylhexa-1,5-dienes

A Non-Cope among the Cope Rearrangements of 1,3,4,6-Tetraphenylhexa-1,5-dienes

Electron bridges in the mechanisms of chromic acid oxidation of alcohols

Using NMR Spectroscopy and Chemical Synthesis to Establish Diastereoselectivity of NaBH₄ and Meerwein–Ponndorf–Verley (MPV) Reduction of (±)-Benzoin Isopropyl Ether: A Collaborative Discovery-Based Laboratory Experiment

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A Modified Method for the Meerwein-Ponndorf-Verley Reduction

Cited by 11 publications

References 0 publications

A Non-Cope among the Cope Rearrangements of 1,3,4,6-Tetraphenylhexa-1,5-dienes

A Non-Cope among the Cope Rearrangements of 1,3,4,6-Tetraphenylhexa-1,5-dienes

Electron bridges in the mechanisms of chromic acid oxidation of alcohols

Using NMR Spectroscopy and Chemical Synthesis to Establish Diastereoselectivity of NaBH4 and Meerwein–Ponndorf–Verley (MPV) Reduction of (±)-Benzoin Isopropyl Ether: A Collaborative Discovery-Based Laboratory Experiment

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Product

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Using NMR Spectroscopy and Chemical Synthesis to Establish Diastereoselectivity of NaBH₄ and Meerwein–Ponndorf–Verley (MPV) Reduction of (±)-Benzoin Isopropyl Ether: A Collaborative Discovery-Based Laboratory Experiment