Bridging regioselectivity in triplet-sensitized di-.pi.-methane photorearrangements of ortho-substituted benzonorbornadienes. A case for the importance of benzene HOMO and LUMO polarization

Santiago, Cielo; Houk, K. N.; Snow, Robert A.; Paquette, Leo A.

doi:10.1021/ja00439a066

Cited by 13 publications

(12 citation statements)

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“…One approach could be to couple the isomerization reaction with loss of aromaticity of a fused benzene ring as shown for the benzo-fused couple 1 NBD /1 QC in Scheme 1. Yet, irradiation of derivatives of 1 NBD with various substituents at the benzene ring did not result in QC formation but instead in rearrangement reactions [8][9][10]. Along this line, some of us recently investigated benzo-fused dihydroazulene/vinylheptafulvene (DHA/VHF) derivatives [11,12].…”

Section: Introductionmentioning

confidence: 99%

Donor-Acceptor Substituted Benzo-, Naphtho- and Phenanthro-Fused Norbornadienes

et al. 2020

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The photochromic norbornadiene/quadricyclane (NBD/QC) couple has found interest as a molecular solar thermal energy (MOST) system for storage of solar energy. To increase the energy difference between the two isomers, we present here the synthesis of a selection of benzo-fused NBD derivatives that contain an aromatic unit, benzene, naphthalene or phenanthrene, fused to one of the NBD double bonds, while the carbon atoms of the other double bond are functionalized with donor and acceptor groups. The synthesis protocols involve functionalization of benzo-fused NBDs with bromo/chloro substituents followed by a subjection of these intermediates to a cyanation reaction (introducing a cyano acceptor group) followed by a Sonogashira coupling (introducing an arylethynyl donor group, -C≡CC6H4NMe2 or -C≡CC6H4OMe). While the derivatives have good absorption properties in the visible region (redshifted relative to parent system) in the context of MOST applications, they lack the ability to undergo NBD-to-QC photoisomerization, even in the presence of a photosensitizer. It seems that loss of aromaticity of the fused aromatics is too significant to allow photoisomerization to occur. The concept of destroying aromaticity of a neighboring moiety as a way to enhance the energy density of the NBD/QC couple thus needs further structural modifications, in the quest for optimum MOST systems.

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Section: Introductionmentioning

confidence: 99%

Donor-Acceptor Substituted Benzo-, Naphtho- and Phenanthro-Fused Norbornadienes

et al. 2020

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“…The remarkable regioselectivity of the triplet di-ir-methane rearrangements of benzonorbornadienes,2-5 summarized in Scheme I, has been satisfactorily explained by qualitative theoretical treatments. 3,6 The investigation reported here was undertaken, in part, to provide quantitative information about the orbital energies in these systems and thus to quantitate the theory of regioselectivity in photorearrangements of benzonorbornadienes.…”

Section: Introductionmentioning

confidence: 99%

Photoelectron spectra of ortho- and meta-substituted benzonorbornadienes. Relationships to regioselectivities in triplet di-.pi.-methane rearrangements

Santiago¹,

McAlduff²,

Houk³

et al. 1978

J. Am. Chem. Soc.

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“…The reaction mixture was heated at reflux overnight (12 h), cooled to 25 °C, filtered through a pad of Celite, and evaporated. The resulting brown oil upon distillation gave 7.82 (cyclohexane) 285.5 nm (e 1270), 282 sh (1260), 277.5 (1300), and 213 (23 000); <5Me4s¡ (CC14) 6.96-6.31 (m, 5), 4.16 (m, 1), 3.82 (m, 1), 3.74 (s, 3) and 2.18 (m, 2). The analytical sample was isolated by preparative VPC on column A31 (150 °C).…”

Section: Methodsmentioning

confidence: 99%

“…The organic phase was separated, washed with water (2 X 100 mL), dried, filtered, and evaporated. The residual oil was distilled to give 2.94 g (88%) of 18 which was further purified by preparative VPC on column A31 (150 °C): vm:,x (neat) 2985, 2940, 2235, 1465, 1419, 1304, 1226,810, 790, 766, 740, and 725 cm-1; ,,,.,x (cyclohexane) 212 nm (e 26 000), 284 (2060), and 292 (2160): 6yic4s¡ (CC14) 7.42-6.62 (m, 5), 4.07 (m, 1), 3.88 (m. 1), and 2.18 (in. 2).…”

Section: -Cyanobenzonorbornadiene (18)mentioning

confidence: 99%

“…Hydrolysis was effected by heating at the reflux temperature for 4 h. Cooling, separation of the layers, and extraction of the aqueous phase with ether (3X15 mL) gave a combined organic solution which was washed with an equal volume of water, dried, filtered, and evaporated. Molecular distillation of the residue at 110 °C (0.02 mm) and preparative VPC purification on column A31 afforded 410 mg (75.7%) of 19: vmax (neat) 1679 cm-1; ¿Me4Si (CC14) 7.33-6.55 (m, 5), 4.74 (m, 1), 3.79 (m, 1), 2.44 6-Nitroanthranilic Acid ( 21), Toa solution of 20 (9.6 g, 0.05 mol) in 1 N potassium hydroxide solution (50 mL) cooled to 5 °C was added an ice-cooled solution of bromine (2.5 mL, 0.05 mol) dissolved in 100 mL of 1 N potassium hydroxide followed by an additional 150 mL of the alkali. The mixture was heated with stirring on a steam bath for 80 min, cooled, and treated with 2 N hydrochloric acid (100 mL).…”

Section: -Acetylbenzonorbornadiene (19)mentioning

confidence: 99%

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Demonstration and analysis of bridging regioselectivity operative during di-.pi.-methane photorearrangement of ortho-substituted benzonorbornadienes and anti-7,8-benzotricyclo[4.2.2.02,5]deca-3,7,9-trienes

Snow¹,

Cottrell²,

Paquette³

1977

J. Am. Chem. Soc.

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The triplet-state photoisomerizations of a number of ortho-substituted benzonorbornadienes and anti-7,8-benzotricycl0[4.2.2.0~~~]deca-3,7,9-trienes are reported. All of the examples studied underwent di-r-methane rearrangement with preferential benzo-vinyl bridging to the adjacent aryl carbon. For the nitro-and acetylbenzonorbornadienyl cases, the rearrangement was regiospecific. When the substituent group was cyano (96%), methoxy (89.3%), amino (82.6%), methyl (70%), or fluoro (50%), the bonding preference was somewhat less dramatic (degree of ortho bridging given in %). Sensitized irradiation of o-methoxybenzotricyclodecatriene 27 gave rise to a 66:10:24 mixture of 38-OCH3, 39-OCH3, and 40-OCH3. In contrast, cyano derivative 29 afforded an 84:8:8 mixture of 38-CN, 39-CN, and 40-CN. The diminished level of vinyl-vinyl bonding in the latter case ( I 1-12:l vs. 3:l) denotes that concentration of triplet energy in the aromatic moiety promotes benzo-vinyl bridging. The observed regioselectivity is shown to conform to the magnitude of the relevant orbital coefficients as calculated by perturbation theory and supported by PE data.In the preceding paper,' we delineated the striking control exerted by meta substituents on the directionality of benzovinyl bonding from the triplet excited states of benzonorbornadienes and anti-7,8-benzotricycl0[4.2.2.0~~~]deca-3,7,9-trienes. In the case of a n acceptor substituent, fully regiospecific para bridging was observed with ultimate formation of 2. As concerns donor substituents, a marked predilection for

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Bridging regioselectivity in triplet-sensitized di-.pi.-methane photorearrangements of ortho-substituted benzonorbornadienes. A case for the importance of benzene HOMO and LUMO polarization

Cited by 13 publications

References 2 publications

Donor-Acceptor Substituted Benzo-, Naphtho- and Phenanthro-Fused Norbornadienes

Donor-Acceptor Substituted Benzo-, Naphtho- and Phenanthro-Fused Norbornadienes

Photoelectron spectra of ortho- and meta-substituted benzonorbornadienes. Relationships to regioselectivities in triplet di-.pi.-methane rearrangements

Demonstration and analysis of bridging regioselectivity operative during di-.pi.-methane photorearrangement of ortho-substituted benzonorbornadienes and anti-7,8-benzotricyclo[4.2.2.02,5]deca-3,7,9-trienes

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