Photochemical [2 + 2] Cycloadditions. IV. Cycloaddition of 2-Cyclopentenone to Some (omega--1)-Alken-1-ols; Evidence for Regioselectivity due to Hydrogen Bonding.

Sydnes, Leiv K.; Hansen, Kjersti I.; Oldroyd, D. L.; Weedon, Alan C.; Jørgensen, Even H.; Coppens, Philip; Buchardt, Ole

doi:10.3891/acta.chem.scand.47-0916

Cited by 22 publications

(12 citation statements)

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“…Its directing capability has been invoked to explain the preference for the HH-isomer in the reaction of cyclopentenone and various alkenols in pentane. 21 Similar conclusions were drawn from the course of the photocycloaddition of thymine and a coumarin derivative of Kemp's triacid in benzene. 22 The question of stereochemical integrity with regard to the double-bond geometry in the cyclic enone and in the alkene is linked to the mechanism of the cycloaddition.…”

Section: Methodssupporting

confidence: 52%

“…The chiral alkenone 20 exists in two half chair conformations the more stable of which ideally accomodates cyclobutane formation anti to the methyl group as 1,2-synclinal and 1,3-diaxial interactions are minimized (Scheme 9). Only a single product (21) was obtained in excellent yield. 55 In other examples the diastereoselectivity in favor of one isomer was less pronounced.…”

Section: Methodsmentioning

confidence: 99%

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Stereoselective Intermolecular [2 + 2]-Photocycloaddition Reactions and Their Application in Synthesis

Bach

1998

Synthesis

300

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Stereoselective intermolecular [2+2]-photocycloaddition reactions of alkenes and Paternò-Büchi reactions are reviewed. For both reactions the regioselectivity and the simple diastereoselectivity which are relevant to the formation of a single product isomer are explained based on representative examples. In the subsequent sections the facial diastereoselectivity induced by the respective reaction partner is treated. Particular emphasis is given on synthetic applications of the cyclobutanes and oxetanes obtained by the photochemical key step. Consecutive reactions are discussed and the potential use of the four-membered ring intermediates is highlighted.

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Section: Methodssupporting

confidence: 52%

Section: Methodsmentioning

confidence: 99%

Stereoselective Intermolecular [2 + 2]-Photocycloaddition Reactions and Their Application in Synthesis

Bach

1998

Synthesis

300

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“…It was unambiguously shown that the two hydrogen bonds which form between the lactam part of dihydropyridone 1 and the lactam unit of the aldehyde are responsible for the observed face discrimination. This discovery represented the first example for facial stereocontrol in an intermolecular 16 photochemical reaction by hydrogen bonds, and it has spurred increased interest in the use of hydrogen bonds as a control element in photochemical processes . For us, the discovery proved that it should be possible to use systems related to 2 as chiral complexing agents.…”

Section: Introductionmentioning

confidence: 99%

Highly Enantioselective Intra- and Intermolecular [2 + 2] Photocycloaddition Reactions of 2-Quinolones Mediated by a Chiral Lactam Host: Host−Guest Interactions, Product Configuration, and the Origin of the Stereoselectivity in Solution

et al. 2002

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The [2 + 2] photocycloaddition of 4-alkoxy-2-quinolones was conducted in the presence of the chiral lactams 5 or ent-5. At -60 degrees C in toluene as the solvent the intramolecular reaction of quinolones 6 and 8 as well as the intermolecular photocycloaddition of various alkenes 13 to quinolone 12 proceeded with excellent enantioselectivity (81-98% ee) and in high yields (61-89%). Styrene (13d) reacted sluggishly in the intermolecular reaction (29% yield, 83% ee). The absolute configuration of the intramolecular photocycloaddition products 7 and 9 was elucidated by single-crystal X-ray crystallography of the corresponding diastereomeric N-menthyloxycarbonyl derivatives. The relative configuration of the intermolecular photocycloaddition products 14 and 15 was assigned on the basis of NOESY experiments and on crystallographic evidence. The differentiation of the enantiotopic faces in the prochiral quinolones 6, 8, and 12 can be explained by assuming a coordination of these substrates to the lactams 5 or ent-5 via two hydrogen bonds. Upon binding to 5 the si-face is shielded by the bulky tetrahydronaphthalene backbone, and the re-face is exposed to an intra- or intermolecular attack. On the basis of the association constant (K(a)) for the coordination of quinolone to host 5 an interpretation of the observed enantiomeric excess has been put forward. The parent quinolone 17 was employed as substrate for microcalorimetric and NMR titration experiments. From the data obtained for K(a) and DeltaH(a) the expected enantiomeric excess was calculated for two given temperatures (-15 and -60 degrees C). The calculated values fit the observed data within reasonable limits and prove that two-point hydrogen bonding can be sufficient to achieve a preparatively useful face differentiation in solution phase photochemistry.

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“…We could recently show that [2 + 2]-photocycloaddition reactions of quinolones proceed in the presence of chiral lactams as host compounds with high enantioselectivity . The hosts bind to the substrate via two hydrogen bonds , and provide the steric bias to shield one of the stereoheterotopic faces efficiently . In a similar fashion 2-pyridones should be capable of hydrogen binding to these hosts .…”

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confidence: 99%

Enantioselective Photochemical Reactions of 2-Pyridones in Solution

2001

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[reaction: see text] Two key photochemical reactions of prochiral 2-pyridones were studied in the presence of a chiral host. The [4 + 4]-photocycloaddition with cyclopentadiene (CpH) proceeded smoothly and with high enantioselectivity (84-87% ee). The absolute configuration of the endo-diastereoisomer was established by X-ray crystallography. The electrocyclic [4pi]-ring closure to 3-oxo-2-azabicyclo[2.2.0]-5-hexenes occurred with lower enantioselectivity (20-23% ee at -20 degrees C). The velocity of the latter reaction slowed significantly with decreasing temperature.

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Photochemical [2 + 2] Cycloadditions. IV. Cycloaddition of 2-Cyclopentenone to Some (omega--1)-Alken-1-ols; Evidence for Regioselectivity due to Hydrogen Bonding.

Cited by 22 publications

References 0 publications

Stereoselective Intermolecular [2 + 2]-Photocycloaddition Reactions and Their Application in Synthesis

Stereoselective Intermolecular [2 + 2]-Photocycloaddition Reactions and Their Application in Synthesis

Highly Enantioselective Intra- and Intermolecular [2 + 2] Photocycloaddition Reactions of 2-Quinolones Mediated by a Chiral Lactam Host: Host−Guest Interactions, Product Configuration, and the Origin of the Stereoselectivity in Solution

Enantioselective Photochemical Reactions of 2-Pyridones in Solution

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