Investigating the Arenyl-Diene Double [3+ 2] Photocycloaddition Reaction (original) (raw)
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Tetrahedron letters, 1996
The first cis, cis, cis, trans-[5.5.5.5]-fenesttanes have been synthesized in three steps using a novel arene-alkene photocycloaddition-rsdical cyclir.ation cascade, which creates overall 5 new rings and 8 stereogenic centers. A lead tetraaeetate mediated ring expansion of a 5,5-fused ring system, discovered in the course of exploring the chemistry of these new materials, is also described.
Tetrahedron letters, 1996
The first cis, cis, cis, trans-[5.5.5.5]-fenesttanes have been synthesized in three steps using a novel arene-alkene photocycloaddition-rsdical cyclir.ation cascade, which creates overall 5 new rings and 8 stereogenic centers. A lead tetraaeetate mediated ring expansion of a 5,5-fused ring system, discovered in the course of exploring the chemistry of these new materials, is also described.
2012
In 2008 Takeya and co-workers reported on the isolation and structural elucidation of the [5.3.1]propellane-containing and biologically active neoclerodane salvileucalin B (1, ). In connection with efforts to probe the origins of the cytotoxic effects of this natural product, we recently developed a synthesis of the key substructure 2. Part of the associated reaction sequence involved reduction of nitrile 3 to primary alcohol 4. This proved to be an unexpectedly complex process because of the intervention of remarkable and reversible cyclopropane ring-cleavage processes leading to the formation (and disassembly) of aza-and oxa-[5.6.5.6]fenestratetraenes. These compounds represent unusual new examples of fenestranes that, as a class, continue to attract considerable attention because of the capacity they provide to examine the "plasticity" of the tetrahedral geometry normally imposed on sp 3 -hybridized carbon atoms by virtue of the bonding in such systems. Details are presented herein.
Journal of the American Chemical Society, 1969
A means of generating the zwitterionic species postulated as reaction intermediates in dienone photochemistry was developed. This involved synthesis of 2-bromo-6,6-diphenylbicyclo[3.1 .O]hexan-3-one and 2,4-di-brom0-6,6-diphenylbicyclo[3.1 .O]hexan-3-one. Treatment of the monobromo ketone with potassium t-butoxide or the dibromo ketone with zinc afforded the Type A rearrangement product, 6,6-diphenylbicyclo[3.1 .O]hex-3-en-2-one in a process postulated as proceeding via the zwitterionic species of the photochemical process. 6-endo-Phenyl-6exo-p-bromophenyl bicyclo[3.1 .O]hexan-Zone, 6-exo-phenyl-6-endo-p-bromophenylbicycl0[3.1 .O]hexan-2-one, 6endo-phenyl-6-exo-p-bromophenylbicyclo[3.l.0]hexan-3-one, 6-exo-phenyl-6-endo-p-bromophenylbicyclo[3.1.0]hexan-3-one were synthesized and their configurations were interrelated. Reaction of 2-bromo-6-endo-phenyl-6exo-p-bromophenylbicyclo[3.1 .O]hexan-3-one with potassium t-butoxide in t-butyl alcohol afforded 6-endo-phenyl-6-exo-p-bromophenylbicyclo[3.l.0]hex-3-en-2-one. Similarly, under these reaction conditions, 2-bromo-6-exophenyl-6-endo-p-bromophenylbicyclo[3.l.O]hexan-3-one gave stereospecifically 6-exo-phenyl-6-end~-p-bromophenylbicyclo[3.l.0]hex-3-en-2-one. In analogy to the stereochemistry of the santonin to lumisantonin rearrangement, the dark reaction of the bromo ketones proceeded with inversion of configuration at the benzhydryl carbon which migrates by a "slither" rather than a pivot mechanism. The stereochemical course is rationalized on a molecular orbital basis.
Journal of The Chemical Society-perkin Transactions 1, 1992
The photochemistry of 4-phenoxybut-1 -ene is markedly influenced by the presence and position of electron-withdrawing substituents on the benzene ring. A cyano substituent in the 2'-or 4'-position promotes an efficient intramolecular cycloaddition to give good yields of the 4-oxatricyclo-[7.2.0.03*7] undeca-2,lO-dienes, by way of the photolabile 1 1 -oxabicyclo[6.3.0] undeca-l,3,5-triene, the precursor of which is presumed to be a thermally labile intramolecular ortho photocycloadduct. The 3'-cyano isomer reacts inefficiently and only the 2'-isomer in the methoxycarbonyl series undergoes the photocycloaddition. The formation of the trienes is efficiently quenched by 1,3-dienes but their intramolecular cyclisation is unaffected by the presence of the triplet quenches.
Journal of Organic Chemistry, 1985
The thermolysis and 350-nm and 185-nm photolyses of the azoalkanes 2,3-diazabicyclo[2.2.l]hept-2-ene (la) and spiro[cyclopropane-1,7'-[2,3]diazabicyclo[2.2.l]hept-2-ene] (lb) have been investigated. The exo/endo stereochemistry in the bicyclo[2.l.Q]pentanes 2a,b and in the rearranged olefin 3b w a~ determined by deuteration experiments using 5,6-exo-dideuterioazoalkanes la,b-d2. Whereas thermal and direct photochemical (350 nm; n, T * ) denitrogenation of azoalkane la-d2 led exclusively (>99%) to bicyclo[2.1.0]pentane 2a-dz with preferential (1.54, 2.94) double inversion, the triplet-sensitized photolysis afforded nearly complete stereoequilibration. In 185-nm denitrogenation an unexpectedly high exo/endo ratio (3.1) for bicyclo[2.1.O]pentane 2a-d, was found, besides isomerization to cyclopentene 2a-dz. Similar results were obtained in the denitrogenation of spiroazoalkane lb-d2, which exhibited exo stereochemical preferences in both photoproducts spiro[bicyclo[2.1.0]pentane-5,1'cyclopropane] 2b-d2 and bicyclo[3.2.0]hept-l-ene 3b-d2. The 350-nm photolysis of azoalkane lb-d, gave preferential formation of ezo-spirobicyclo[2.1.O]pentane 2b-d2 and exo-olefin 3b-d2, whereas triplet-sensitized decomposition yielded almost complete loss of stereochemical preference in the olefin 3b-dz. The 185-nm photolysis of azoalkane lb-d2 showed similar behavior compared with the azoalkane la, e.g., a t high exo/endo ratio in spirobicyclo-[Z.l.O]pentane 2b-d2. Also olefin 3b was formed with complete stereoequilibration. These diverse experimental results are discussed in terms of one-bond vs. two-bond cleavage processes leading to the diazenyl diradicals D'n,,,
Flavin-Mediated Visible-Light [2+2] Photocycloaddition of Nitrogen- and Sulfur-Containing Dienes
European Journal of Organic Chemistry, 2017
The [2+2] photocycloaddition mediated by 1-butyl-3-methyl-7,8-dimethoxyalloxazine (1) has been found to be an effective tool for cyclising ω-phenyland ω,ω′-diphenyl-4-aza-1,6-heptadienes, in which the nitrogen atom is protected by acylation or quaternisation, towards the synthesis of a variety of phenyl-and diphenyl-3-azabicyclo[3.2.0]heptanes and their corresponding quaternary salts. Thia derivatives, with the sulfur atom in the form of a sulfone group, underwent an analogous cyclisation. Advantageously, visible light (400 nm) was used for [a]
Photochemical [2 + 2] Cycloaddition of Acetylene to Chiral 2(5 H )-Furanones
The Journal of Organic Chemistry, 2003
The [2 + 2] photocycloaddition of acetylene to chiral 2(5H)-furanones was investigated. The influence on the chemical yield and facial diastereoselectivity of the substituent at the stereogenic center and also the effect of a 4-methyl group were evaluated. A mechanistic proposal based on a simple theoretical conformational analysis is presented. Using a C 2 -symmetric bis(lactone) as the substrate, a diastereomeric excess higher than 98% was found.