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Abstract
Current methods of urethane preparation from amines invariably involve high-energy and often toxic or cumbersome molecules to make the process exergonic. CO2 aminoalkylation using olefins and amines represents an attractive albeit endergonic alternative. We report a moisture-tolerant method that uses visible light energy to drive this endergonic process (+25 kcal/mol at STP) using sensitized arylcyclohexenes. They convert much of the photon's energy to strain upon olefin isomerization. This strain energy greatly enhances alkene basicity, allowing for sequential protonation by and interception of ammonium carbamates. Following optimization steps and amine scope evaluation, an example product arylcyclohexyl urethane underwent transcarbamoylation with some demonstrative alcohols to form more general urethanes with concomitant regeneration of the arylcyclohexene. This represents a closure of the energetic cycle, producing H2O as the stoichiometric byproduct.
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Affiliation(s)
- Timothy D Schoch
- Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, United States
| | - Jimmie D Weaver
- Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, United States
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2
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Affiliation(s)
- Norbert Hoffmann
- CNRS, Université de Reims Champagne-Ardenne; ICMR, Equipe de Photochimie; UFR Sciences, B.P. 1039 51687 Reims France
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Affiliation(s)
- David I. Schuster
- Department of Chemistry, New York University, New York, New York 10003, United States
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Guerry P, Blanco P, Brodbeck H, Pasteris O, Neier R. 1-Methoxycarbonyl-substituiertes 2,3-Dihydropyridin-4(1H)-on (= Methyl-1,2,3,4-tetrahydro-4-oxopyridin-1-carboxylat) als Chromophor für die photochemische [2 + 2]-Cycloaddition. Helv Chim Acta 2004. [DOI: 10.1002/hlca.19910740118] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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García-Expósito E, Alvarez-Larena A, Branchadell V, Ortuño RM. [2 + 2]-Photocycloaddition of 1,1-Diethoxyethylene to Chiral Polyfunctional 2-Cyclohexenones. Regioselectivity and π-Facial Discrimination. J Org Chem 2004; 69:1120-5. [PMID: 14961660 DOI: 10.1021/jo035532n] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photochemical [2 + 2]-cycloadditions of 1,1-diethoxyethylene to chiral polyfunctional 2-cyclohexenones have been carried out leading to the production of highly constrained unusual alpha-amino acids with excellent regioselectivity and satisfactory yields. Theoretical calculations have been done to rationalize the observed regio- and diastereoselectivity and show that regiochemistry is determined by the relative rate of formation of the 1,4-biradical intermediates and not by the stability of these species.
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Affiliation(s)
- Frederick D. Lewis
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113
| | - Weizhong Liu
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113
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Schuster DI, Yang JM, Woning J, Rhodes TA, Jensen AW. Mechanism of acid-catalyzed photoaddition of methanol to 3-alkyl2-cyclohexenones. CAN J CHEM 1995. [DOI: 10.1139/v95-247] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Contrary to a previous report, it is concluded that formation of methanol adducts to 3-methyl-2-cyclohexenones and of deconjugated enones on irradiation of the enones in acidified solutions proceeds via protonation of the intermediate enone π,π* triplet excited state and not by protonation of a relatively long-lived ground state trans-cyclohexenone. A rate constant for protonation of the triplet state of 3-methyl-2-cyclohexenone by sulfuric acid of 1.7 × 109 M−1 s−1 was determined by laser flash photolysis in ethyl acetate. Based on quantum efficiencies of product formation, a rate constant of ca. 108 M−1 s−1 was estimated for protonation of the enone triplet by acetic acid, which is too small to cause measurable reduction in the triplet state lifetime in the mM concentration range used in the preparative studies. The intermediate carbocation can be trapped by methanol, or revert to starting enone or the exocyclic deconjugated enone by loss of a proton. Since products revert to starting materials in an acid-catalyzed process, there is an acid concentration at which the yields of products are optimal. This concentration is ca. 6 mM for acetic acid, but is only 0.1 mM for p-toluenesulfonic or sulfuric acids. Product formation could be quenched using 1-methylnaphthalene and cyclopentene as triplet quenchers; in the latter case, formation of [2 + 2] photoadducts was observed to compete with formation of methanol adducts. Quenching rate constants were determined by laser flash studies. Keywords: laser flash photolysis, kinetic absorption spectroscopy (KAS), photoacoustic calorimetry (PAC), protonation of triplet states, trans-cyclohexenones.
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Chow YL, Cheng XE. The reaction pattern of norbornene with excited state carbonyl compounds: Photochemical preparations of norbornene derivatives. Res Chem Intermed 1993. [DOI: 10.1163/156856793x00082] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Dwyer L, Crocker P, Watt D, Vanaman T. The effects of calcium site occupancy and reagent length on reactivity of calmodulin lysyl residues with heterobifunctional aryl azides. Mapping interaction domains with specific calmodulin photoprobe derivatives. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)41716-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Samuel CJ, Beaton HG, Davey K, Reader C. Photocycloadditions to a pyrone analogue. J Photochem Photobiol A Chem 1991. [DOI: 10.1016/1010-6030(91)87049-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Abstract
Energies and lifetimes of triplet states of a series of 2-cyclohexenones have been measured in solution under ambient conditions by time-resolved photoacoustic calorimetry (PAC). The PAC triplet lifetimes are in excellent agreement with lifetimes measured by kinetic absorption spectrophotometry (KAS) using nanosecond flash techniques, indicating that the present data indeed pertain to the enone triplets previously studied using KAS. The data demonstrate that, as previously proposed, the pi pi triplet energies in these systems are indeed correlated with triplet lifetimes, and vary sensibly with the anticipated extent of conformational flexibility of the C = C bond. No evidence supporting formation of metastable trans-cyclohexenones was obtained. The data also demonstrate greater precision and, for lifetimes, greater accuracy than has hitherto been claimed for the PAC technique for study of transients with lifetimes in the 25 ns range.
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Affiliation(s)
- D I Schuster
- Department of Chemistry, New York University, NY 10003
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Kumar M, Rao JM. Effect of micellar medium on photoannelation vs energy transfer in the system excited cyclohex-2-en-1-one-cyclopentadiene. Tetrahedron 1990; 46:5383-5388. [DOI: 10.1016/s0040-4020(01)87845-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Swapna G, Lakshmi A, Rao JM, Kunwar A. Mechanistic implications of photoannelation reaction of 4,4dimethyl-cyclohex-2-ene-1-one and acrylonitrile — regio and stereochemistry of the major photoadduct by 1H and 13C NMR spectroscopy. Tetrahedron 1989. [DOI: 10.1016/s0040-4020(01)80042-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Demuth M, Pandey B, Wietfeld B, Said H, Viader J. Photocycloadditions of 2-(trimethylsilyloxy)-1,3-butadiene to 2-cycloalkenones. Access to the basic pentalenolactone skeleton. Helv Chim Acta 1988. [DOI: 10.1002/hlca.19880710603] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Wintgens V, Guérin B, Lennholm H, Brisson J, Scaiano J. Photochemistry of the inclusion complex of (R-)Δ1,9-10-methyl-2-octalone with α-cyclodextrin. J Photochem Photobiol A Chem 1988; 44:367-73. [DOI: 10.1016/1010-6030(88)80107-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Cruciani G, Semisch C, Margaretha P. Influence of substituents on C(6) of 4,4-dimethyl-2-cyclohexanone on photoaddition vs. photocycloaddition to 2-methylpropane. J Photochem Photobiol A Chem 1988. [DOI: 10.1016/1010-6030(88)80094-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Mintas M, Schuster DI, Williard PG. Stereochemistry and mechanism of the [2 + 2] and [4 + 2] photocycloaddition of alkenes and dienes to pummerer's ketone. Tetrahedron 1988. [DOI: 10.1016/s0040-4020(01)89788-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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