Photochemical synthesis. XXV. Photochemical cycloaddition. Some applications of the use of enolized .beta.-diketones

Challand, B. D.; Hikino, H.; Kornis, Gabe I.; Lange, Gordon L.; Mayo, P. De

doi:10.1021/jo01256a006

Cited by 91 publications

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“…[2] at [ 0 ] = 1 M to give eqs. [5] and [6], respectively. The values of M and N can be obtained by using the 6, values determined for 3 and 6 at [DBMBF2] = 0.01 and 0.07 M given in Table 3, from which M = 0.53, N = 0.04 for 3, and M = 0.13, N = 0.69 for 6 are obtained (see Table 5).…”

Section: Discussionmentioning

confidence: 99%

“…The relative contributions of these two quantum yields can be calculated from the first and second terms, respectively, in eqs. [5] and [6] for these two olefins. As shown in Table 6, the photocycloaddition pattern for acyclic olefin 3 is clearly different from that for cyclic olefin 6.…”

Section: Discussionmentioning

confidence: 99%

“…It was noted that the Io/I points monitored at either 398 or 416 nm were correlated by a single straight line, and that the slopes (= experimental k,z;) decreased when quenching experiments were carried out at higher DBMBF2 concentrations (Table 4) are computed from eqs. [5] and [6]. 'The k,~, was obtained from the monitor of cycloaddition quantum yields.…”

Section: Fluorescence Quenchingmentioning

confidence: 99%

“…i.e., I' is equivalent to the term of lo(ex) t Io(mono)/I(mono) (31). The plot of I'/I for cycloheptene revealed that the quenching efficiency of the excimer as represented by the slope was k,~, = 6.77 M-I if the point of [6] = 0.329 M was ignored; at this high concentration, extensive quenching caused a large margin of error due to weak excimer emission. Under the same procedure, it was shown that the excimer intensities were feebly quenched by 3; the slope was about 0.4 M-I.…”

Section: Fluorescence Quenchingmentioning

confidence: 99%

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The dual pathway in photocycloaddition of 1,3-diketonatoboron difluorides: excimer reactions

Chow¹,

Xiang²

1991

Can. J. Chem.

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. Can. J. Chem. 69, 1575 (1991).The lowest singlet excited state of dibenzoylmethanatoboron difluoride DBMBF2, a model compound of the BF2 complexes of 1.3-diketones, reacted with various simple olefins to give regiospecific and stereospecific photocycloadducts of 1,5-diketones similar to those from the de Mayo type reaction. DBMBFz in acetonitrile exhibited two discrete fluorescences at 398 and 416 nm for the monomer and at 522 nm for the excimer; they were both quenched, but in different proportions, by a simple olefin. An "oxygen test" showed that the excimer of DBMBF2 is formed irreversibly in acetonitrile. The quantum yields of the photocycloaddition were shown to be proportional not only to olefin concentrations but also to DBMBF2 concentrations. Kinetic analysis has established that the total quantum yield is the sum of those arising from the interactions of the singlet excited DBMBF2 and its excimer, respectively, with an olefin, i.e., the sum of the quantum yields of exciplex and triplex pathways. The contributions from the two pathways are determined by the type of olefins and the range of DBMBFz concentrations. For endocyclic olefins, the triplex pathway is more important and the corresponding photocycloaddition becomes very efficient as soon as the excimer starts to form in [DBMBF2] > 0.001 M. For the monosubstituted olefins, on the contrary, the exciplex pathway is always more important than the triplex pathway; they react primarily from the singlet excited state of DBMBF2.Key words: singlet state photocycloaddition, irreversible excimer formation, excimer cycloaddition, triplex and exciplex reactions. IntroductionIn a preliminary communication (1) we summarized various types of photoreactions displayed by dibenzoylmethanatoboron difluoride (DBMBF2), a representative of the BF2 complexes of 1,3-diketones; they involve photocycloaddition with olefins, sensitization of electron-rich olefins by electron transfer to form cation radicals, exciplex~xcimer formations, and subsequent reactions therefrom. It was proposed that these pho-

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Fluorescence Quenchingmentioning

confidence: 99%

Section: Fluorescence Quenchingmentioning

confidence: 99%

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The dual pathway in photocycloaddition of 1,3-diketonatoboron difluorides: excimer reactions

Chow¹,

Xiang²

1991

Can. J. Chem.

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“…After the demonstration that cyclopentenone adds photochemically to cyclopentene 9 • a mixed strategy which combines this photoaddition with the photoannelation has been used tosynthesizE ß-himachalene 10 Transformation of the unsaturated ketone 8 into a-himachalene' 10 involves the addition of methylmagnesium iodide ta the free carbonyl-funct1on followed by~e stereoselective addition. ci4 with respect to the hydro~ group.…”

mentioning

confidence: 99%

Photochemical approach to the synthesis of natural products

Kossanyi¹

1979

Pure and Applied Chemistry

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Abstract. The use of photochemical conversion of one molecule into an other as an approach to fine chemieals showing interest as new synthons, or as a key-step in multiple-steps synthesis of natural products is emphasized. The following topics are reviewed : photocycloaddition (photoannelation, ring-enlargement, access to grandisol, addition of allene to polycyclic enones), intramolecular cyclisation (electrocyclisation of benzylidene urethanes, photolytic cyclodehydrohalogenation, heteroatom directed photoarylation), molecular rearrangement of cross-conjugated cyclohexadienones, ring-opening of cyclanones and conjugated cyclohexadienones into terpenoids, formation and thermal decomposition of oxetanes, functional transformations.The use of photochemistry as a tool either for a single transformation or as a key step in a multiple-steps sequence has received a large attention in the past ten years. It is not the goal of this article to review the industrial applications of photochemistry since this aspect has already been developped by eminent specialists1 ; but rather to describe the synthetic approach towards fine chemieals using a photochemical transformation as a key step in a multiple-step reaction sequence. The principal reactions which will be dealt with are concerned with intermolecular photocycloaddition (oxetanes formation, photoannelation, ring-enlargement, access to grandisol, addition of allene to polycyclic enones), intramolecular cyclisation (a-diketones, benzylidene urethanes, cyclodehydrohalogenation and hetero-atom directed arylation) which has been used mainly to prepare alkaloids, molecular rearrangement of cross conjugated cyclohexadienones into bicyclo [3.1.0] hexenone intermediates, ring-opening of cyclanones according to the NORRISH type I reaction and of conjugated cyclohexadienones to form terpenoid-like compounds and, at last, functional transformations-(such as elimination of blocking groups). I INTERMOLECULAR PHOTOCYCLOADDITIONS.The photochemical cycloaddition which forms four-membered ring compounds has been widely used to prepare natural products. In most cases, the light-induced reaction is only one step but the key of a multiple steps synthesis. Since four-membered ring compounds are of difficult access from ionic reactions, photochemistry appears to be the most suitable for their preparation. The few examples which follow demonstrate the variety of this type of reaction.a-and ß-bourbonenes (3 and 4 respectively) which are important compo2eijtS of Genanium Bounbon oil and men-tha. p-i.peJvi;t'ä have-been obtained by three different methods -, one of which3 invol .. ves the photocycloaddition of 3-isopropyl-1-methylcyclopentene to cyclopentenone. The obtained adducts have correct anti conformation with the ~-fused junctions but the two head-tohead and head-to-tail isomers 1 and 2 are formed in almest equal proportians beside cyclopentenone dimers. Wittig's reactiön transforms 1 in one step into ß-bourbonene 4, while addition of methyllithium followed with acid-catalyzea dehydration...

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Enone Olefin [2 + 2] Photochemical Cycloadditions

Crimmins

Reinhold

1993

Organic Reactions

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The photochemical [2 + 2] cycloaddition reaction of alkenes to enones, the light‐induced cycloaddition of an excited state enone to a ground state alkene to produce a cyclobutane, is a highly useful reaction in organic synthesis since two new carbon–carbon bonds are formed and a maximum of four new stereogenic centers are introduced into the molecule in the process. The first [2 + 2] photocycloaddition reaction was reported by Ciamician in 1908 when he observed the formation of carvone camphor on exposure of carvone to sunlight for one year. After confirmation of this finding in the late 1950s numerous investigators immediately recognized the value of the reaction for the rapid construction of complex molecular frameworks. The photocycloaddition of a series of Diels–Alder adducts of various dienes and benzoquinones to efficiently produce complex caged structures was subsequently carried out. This included the cycloaddition of a diketone to form a diketone. Meanwhile, a similar photochemical cycloaddition of an enone was utilized in a synthesis of the platonic solid cubane. Shortly thereafter investigations of the intermolecular reaction were initiated through a study of the dimerization of cyclopentenone and the photocycloaddition of cyclopentenone to cyclopentene. Further investigation of the various synthetic and mechanistic aspects of the photocycloaddition resulted in several total syntheses, including caryophyllene and bourbonene, as well as a proposed mechanistic rationale for the reaction. As a result of this pioneering work, largely by Eaton, Corey, and De Mayo, numerous natural and nonnatural products have been prepared by synthetic routes which have a [2 + 2] photocycloaddition as a crucial step in their synthesis. Through further refining over the last 15–20 years, the photocycloaddition reaction has become recognized as an important transformation in the repertoire of the synthetic organic chemist. Both the intermolecular and intramolecular versions of the reaction have been extensively studied. The intramolecular photocycloaddition, like the intramolecular variation of many reactions, has been the subject of much recent work. It is generally thought to be more predictable with regard to regiochemical and stereochemical control, but as will be seen from many of the examples in this chapter, the intermolecular reaction can be highly selective and predictable if the proper reaction participants and conditions are chosen. This chapter reviews the literature on the enone olefin [2 + 2] photocycloaddition since its discovery. Because of the volume of work in the field, there will undoubtedly be some omissions. Examples of all the major types of enone alkene photocycloadditions have been included so that the reader can get a sense of the historical evolution and the current state of the art. Both the inter molecular and the intra molecular variants of this reaction are treated in this chapter. The reader is also referred to a number of excellent reviews on the inter molecular reaction, the intra molecular reaction, and complete treatments which have appeared.

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Photochemical synthesis. XXV. Photochemical cycloaddition. Some applications of the use of enolized .beta.-diketones

Cited by 91 publications

References 1 publication

The dual pathway in photocycloaddition of 1,3-diketonatoboron difluorides: excimer reactions

The dual pathway in photocycloaddition of 1,3-diketonatoboron difluorides: excimer reactions

Photochemical approach to the synthesis of natural products

Enone Olefin [2 + 2] Photochemical Cycloadditions

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