Tomikazu Kawano

Cycloaromatization of a non-conjugated polyenyne system: Synthesis of 5H-benzo[d]fluoreno[3,2-b]pyrans via diradicals generated from 1-[2-{4-(2-alkoxymethylphenyl)butan-1,3-diynyl}]phenylpentan-2,4-diyn-1-ols and trapping evidence for the 1,2-didehydrobenzene diradical

Non-conjugated tetraynes 1 undergo thermal intramolecular cyclization to non-benzenoid diradicals (23) followed by radical cycloaromatization at 25 °C to provide 7-dehydro-5H-benzo[d]fluoreno[3,2-b]pyran monoradical (24) and alkyl radicals (25). Hydrogen abstraction of 24 gives 5H-benzo[d]fluoreno[3,2-b]pyrans (3) which are converted to 4 by reaction with 25. On the other hand, 2 gives 5H-fluorenol (5), indicating the formation of 1,2-didehydrobenzene diradical intermediates (28 and 29). These radicals are trapped as the corresponding Diels-Alder-type products by reaction with an aromatic diene, anthracene.

Biosynthetic Gene-Based Secondary Metabolite Screening: A New Diterpene, Methyl Phomopsenonate, from the Fungus Phomopsis amygdali

The presence of the geranylgeranyl diphosphate synthase (GGS) gene is a common feature of gene clusters for diterpene biosynthesis. We demonstrated identification of a diterpene gene cluster using homology-based PCR of GGS genes and the subsequent genome walking in the fungus Phomopsis amygdali N2. Structure determination of a novel diterpene hydrocarbon phomopsene provided by enzymatic synthesis with the recombinant terpene synthase PaPS and screening of fungal broth extracts with reference to characteristic NMR signals of phomopsene allowed us to isolate a new diterpene, methyl phomopsenonate. The versatility of the gene-based screening of unidentified diterpenes is discussed in regard to fungal genomic data.

Domino thermal radical cycloaromatization of non-conjugated aromatic hexa- and heptaynes: synthesis of fluoranthene and benzo[a]rubicene skeletons

Non-conjugated aromatic hexa- and heptaynes underwent domino thermal radical cycloaromatization at 25°C to yield indenol ring-fused fluoranthene and indenol ring-fused benzo[a]rubicene skeletons with helicity. This multi-cyclization reaction proceeded regioselectively to yield [6]helicene derivatives via annulation at the final step. The structure and thermal racemization of [6]helicene derivatives (6 and 7) is also described.

Multiple cycloaromatization of novel aromatic enediynes bearing a triggering device on the terminal acetylene carbon

Abstract Aromatic enediynes (1) bearing a triggering device on the terminal acetylene carbon undergo thermal cyclization at 25 °C to yield polyphenylene ring systems (6, 9, 13, and 15(16)) giving radical intermediates, dehydrobenzene monoradical (12) and didehydrobenzene biradicals (4 and 14) which may serve as a DNA-cleaving reagent.

An unprecedented arylcarbene formation in thermal reaction of non-conjugated aromatic enetetraynes and DNA strand cleavage

The thermal cyclization of non-conjugated aromatic enetetrayne (4) led to the final products (2 and 10) affording 5 H-12-hydroxybenzo[d]fluoreno[3,2-b]pyran radical (C) and arylcarbene (D) intermediates. DNA strand cleavage was observed.

Thermal radical cyclization of non-conjugated aromatic enyne-allenes: Synthesis of a Cyclobuta[a]naphthalene skeleton

Abstract The thermal cyclization of non-conjugated aromatic enyne-allenes ( 2 ) to form benzobicyclo[4.2.0]octatrienol ( 3 ) provides a simple and convenient procedure for the preparation of a cyclobuta[ a ]-naphthalene skeleton ( 4 ).

Cyclopent-2-en-1-ones from [3+2]-annulation of 3-ethoxycarbonyl-2-propenylidene(triphenyl)-phosphorane and glyoxals: Synthesis of cis-jasmone

3-Ethoxycarbonyl-2-propenylidene(triphenyl)phosphorane (2) reacted with glyoxal monohydrates (5) to give 2-substituted 5-ethoxycarbonylcyclopent-2-en-1-ones (6) by [3+2]-annulation reaction in the presence of a base. Compounds 6 were easily converted to 2-substituted cyclopent-2-en-1-ones by deethoxycarbonylation. An application of the annulation to synthesis of cis-jasmone is also described.

Synthesis of oligo(2-ethynylpyridines): novel building blocks for supramolecular systems

Abstract New oligo(2-ethynylpyridines) 1 are synthesized as novel building blocks for the construction of supramolecular systems by the coupling reaction of the novel dibromopyridines 2 with ethynylpyridines 3 .

Synthesis and Properties of Functionalized [6] Helicenes by the Thermal Domino Radical Cycloaromatization of Acyclic Polyynes

Abstract Non-conjugated aromatic hexaynes and heptaynes undergo thermal domino radical cycloaromatization under mild conditions to yield indenol ring-fused fluoranthene and indenol ring-fused benzo[a]rubicene skeletons with helicity. The structure and thermal racemization of [6]helicene derivatives (12 and 13) are also described.

A FACILE SYNTHESIS OF 5-SUBSTITUTED 2-FURYLACETATES VIA 6-HYDROXY-3-OXO-4-HEXENOATES

Abstract 6-Substituted 3-ethoxy-6-hydroxy-2,4-hexadienoates ( 4 ) which were prepared by reaction of ethyl (4 E )-3-ethoxy-5-formyl-2,4-pentadienoate ( 3a ) with nucleophiles or sodium borohydride reduction of 6-substituted 3-ethoxy-6-oxo-2,4-hexadienoates ( 3b-e ) have been converted in very good yields into 5- substituted 2-furylacetates (5) by treating with 47% HBr in THF.