The chemistry of 2-alkoxy-3,4-dihydro-2H-pyrans. 7. Effect of substituents on the reactivity of various alkyl- and phenyl-substituted 3,4-dihydro-2H-pyrans with tert-butyl hypochlorite

Weber, Giuseppe F.; Hall, Steven R.

doi:10.1021/jo01317a012

Cited by 19 publications

(7 citation statements)

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“…The first fraction, a colorless oil (112 mg), contained a 1:2 mixture of trans- 2-ethoxy-4-methyltetrahydropyran 6f 6 and 7f which was identified by comparison with an authentic sample (see below); 1 H NMR (CDCl 3 ) δ trans- 6f : 0.95 (d, 3H, J = 6.16 Hz), 1.29−1.50 (m, 3H), 1.35 (t, 3H, J = 7.4 Hz), 1.87−1.95 (dm, 1H, J = 13.1 Hz), 2.15−2.28 (m, 1H), 3.45−3.80 (m, 2H), 3.90−4.05 (m, 2H), 5.03 (d, 1H, J = 4.40 Hz). Additional spectral data were similar to those reported previously …”

Section: Methodssupporting

confidence: 87%

“…In this case the coincidence of a number of chemical shifts in the 1 H NMR spectrum of the product mixture made unambiguous structural elucidation impossible, and therefore cis - 6j was independently prepared from the THP ether of cis -3-hydroxycyclopentaneacetic acid (readily prepared from norcamphor , ) as shown in Scheme . The identification of the diastereomers of the tetrahydropyran 6f was accomplished by comparison of the observed NMR spectra with those reported in the literature, while the diastereomers of 6h were similarly identified by comparison of the observed NMR data with those reported for the structurally similar cis- and trans- 2,4-dimethyltetrahydropyrans . A 1D NOE experiment conducted on trans - 6h provided additional confirmation.…”

Section: Resultsmentioning

confidence: 83%

“…Reduction of 4-(2-Bromo-1-ethoxyethoxy)but-1-ene (4f). In a variation of procedure A, a solution of 4f (980 mg, 4.4 mmol) in dry benzene (72 mL) when heated with tributylstannane (1.4 mL, 5.3 mmol) for 18 h gave a complex mixture of products ( 1 H NMR), two of which were tentatively identified as being the diastereomeric 2-ethoxy-4-methyltetrahydropyrans 6f , while the detection of olefinic resonances suggested that the uncyclized product 7f had also been formed. The residue was then subjected to a DBU workup procedure 28 followed by repetitive flash chromatography (15:1 pentane/diethyl ether).…”

Section: Methodsmentioning

confidence: 99%

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Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects

Beckwith

Page

1998

J. Org. Chem.

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The influence of the anomeric effect on radical cyclization has been examined by determining the stereochemical outcome of the ring closure of 10 suitably substituted radicals. The stereochemistry of the products formed from the acyclic precursors 4a-f indicates that for suitably constituted radicals anomeric interactions stabilize pseudoaxially substituted transition structures 14 thus affording products with stereochemistry the reverse of that normally observed.In recent times, the use of free radical reactions for chemical synthesis has grown steadily in popularity as the processes which govern and control their outcomes have become better understood. 1 Intramolecular addition reactions of suitably constituted alkenyl radicals and related species are particularly interesting since they readily afford a variety of ring systems commonly found in many natural products. 1 The advantages offered by such reactions generally include high regioselectivity, modest to good stereoselectivity, 1-5 and high chemoselectivity. [1][2][3][4][5] The highly regioselective exo-cyclization of the hex-5-enyl radical has been intensively studied. The accurate determination of its kinetics 6 has underpinned its widespread use as a mechanistic probe and as a radical clock. 7 Most monosubstituted hex-5-enyl radicals also undergo regioselective exo-cyclization while conforming to the general stereochemical guideline that 1-or 3-substituted radicals afford predominantly cis-disubstituted products, while 2-or 4-substituted radicals give mainly transdisubstituted products. 5 It is now generally accepted that the cyclization behavior of simple hex-5-enyl systems reflects the stereoelectronic demands of the transition structure. [2][3][4][5] The hypothesis that the strain energy engendered in attaining the optimum orbital overlap for 1,6-ring closure outweighs the steric and thermodynamic factors which would otherwise favor six-membered ring formation 2-5 has received support from theoretical analyses 8 and the modeling of transition structures by a combination of molecular orbital and molecular mechanics calculations. 8 These calculations confirm the original hypothesis that the transition structure for 1,5-exo-cyclization of hex-5-enyl radicals and related species resembles cyclohexane in its chair form. 2-5 Hence the stereoselectivity exhibited in the ring closure of monosubstituted hexenyl radicals and related species is seen to arise from the propensity of cyclizations to proceed through the more stable pseudoequatorially substituted cyclohexane-like conformation of the transition structure rather than through its less stable pseudoaxially substituted conformer. 8 Since calculations of the relative selectivities of the cyclized products tend to be overestimated when only axially substituted chairlike structures are considered, it appears that boatlike transition structures might also be involved in some reactions. 4,8 Cyclizations of hex-5-enyl type radicals containing heteroatoms have also been studied. 1,9,10 In general such spec...

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Section: Methodssupporting

confidence: 87%

Section: Resultsmentioning

confidence: 83%

Section: Methodsmentioning

confidence: 99%

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Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects

Beckwith

Page

1998

J. Org. Chem.

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“…To gain insight into what other products were forming, 1 H NMR spectra of the crude reaction mixtures generated using catalysts 5 , 7 , 9 , 10 , and 12 were analyzed. In all cases, the major products were a mixture of 6-hydroxy-2-hexanone ( 27 ) and its lactol 28 , indicating that path 2 in Scheme was being followed when many of the catalysts were used. − The presence of these compounds is consistent with this class of catalysts being generally selective for oxidizing secondary alcohols over primary. ,, …”

Section: Resultsmentioning

confidence: 70%

(Cyclopentadienone)iron-Catalyzed Transfer Dehydrogenation of Symmetrical and Unsymmetrical Diols to Lactones

et al. 2019

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Air-stable iron carbonyl compounds bearing cyclopentadienone ligands with varying substitution were explored as catalysts in dehydrogenative diol lactonization reactions using acetone as both the solvent and hydrogen acceptor. Two catalysts with trimethylsilyl groups in the 2-and 5-positions, [2,5- 2), were found to be the most active, with 2 being the most selective in the lactonization of diols containing both primary and secondary alcohols. Lactones containing five-, six-, and seven-membered rings were successfully synthesized, and no over-oxidations to carboxylic acids were detected. The lactonization of unsymmetrical diols containing two primary alcohols occurred with catalyst 1, but selectivity was low based on alcohol electronics and modest based on alcohol sterics. Evidence for a transfer dehydrogenation mechanism was found, and insight into the origin of selectivity in the lactonization of 1°/2°diols was obtained. Additionally, spectroscopic evidence for a trimethylamine-ligated iron species formed in solution during the reaction was discovered.

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“…Application of RCM to ketal 166 using the Grubb’s generation-I Ru-catalyst 167 leads to the formation of spiroketal 168 , which on subsequent hydrogenation provides the bee pheromone 169 ( Scheme 38 ) [ 88 , 89 ].…”

Section: Asymmetric Total Synthesis Of Natural Spiroketalsmentioning

confidence: 99%

Asymmetric Synthesis of Naturally Occuring Spiroketals

Raju

Saikia

2008

Molecules

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The chemistry of 2-alkoxy-3,4-dihydro-2H-pyrans. 7. Effect of substituents on the reactivity of various alkyl- and phenyl-substituted 3,4-dihydro-2H-pyrans with tert-butyl hypochlorite

Cited by 19 publications

References 3 publications

Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects

Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects

(Cyclopentadienone)iron-Catalyzed Transfer Dehydrogenation of Symmetrical and Unsymmetrical Diols to Lactones

Asymmetric Synthesis of Naturally Occuring Spiroketals

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