Shogo Nakatani

Oxygenation of γ,δ-unsaturated ketones in the presence of thiophenol. Efficient formation of cyclic peroxides.

Abstract γ,δ-Unsaturated ketones were found to be oxygenated in the presence of thiophenol to give the corresponding cyclic peroxides. The electrochemical initiation accelerated the reaction markedly.

Total synthesis of natural (+)-FR900482. 3. Completion of the synthesis

Abstract The title synthesis was accomplished by featuring (i) coupling of the aromatic fragment 2 with the optically active aliphatic fragment 3 to install the requisite carbon unit ( 2+3→4 ); (ii) intramolecular aldol reaction of the highly functionalized dialdehyde 10 to produce the desired eight-membered ring system 11 (10→11); (iii) epimerization of the C-7 position of hydroxy ketone 14 to obtain the correct stereochemistry (14→15); (iv) internal hemiacetal formation of hydroxylamino ketone 23 in situ generated from ketone 22 to construct the requisite tetracyclic ring system 24 (23→24) as key steps.

Total synthesis of an enantiomeric pair of FR900482. 3. Completion of the synthesis by assembling the two segments

Abstract The title synthesis was accomplished by a method which features (i) coupling of the aromatic segment 2 with the enantiomerically pure aliphatic segment 3 to install the requisite carbon unit ( 2+3→4 ); (ii) intramolecular aldol reaction of the highly functionalized dialdehyde 10 to elaborate the desired eight-membered ring system 12 ( 10→12 ); (iii) epimerization at the C-8 position of the hydroxy ketone 15 to obtain the correct stereochemistry ( 15→16 ); (iv) internal hemiacetal formation of the N-hydroxylamino ketone 25 in situ generated from the ketone 24 to construct the requisite tetracyclic ring system 26 ( 24→25→26 ) as the key steps. The in vitro cytotoxicity assay of the synthesized compounds (1, ent-1, 31, ent-31, 32, and ent-32) against P388 murine leukemia cells disclosed that FR900482 (1) and its congeners 31, 32 bearing natural absolute configuration are 100 times more cytotoxic than the corresponding unnatural enantiomers (ent-1, ent-31, ent-32).

STUDIES TOWARD THE TOTAL SYNTHESIS OF ANTIBIOTIC ROSEOPHILIN : A NOVEL SYNTHESIS OF THE MACROTRICYCLIC PART

Abstract The macrotricyclic part of roseophilin, a novel cytotoxic antibiotic, was efficiently synthesized starting with the known 3-formylpyrrole; the method features intramolecular alkylation to form the desired thirteenmembered carbocycle and base-induced intramolecular acylation to construct the requisite pyrrole-fused cyclopentanone ring system as the key steps.

Synthesis of various model compounds for the conjugated heterocyclic ring system of antibiotic roseophilin

Abstract The title synthesis was accomplished starting with 3-chloro-2-formylpyrrole. The synthetic scheme featured one-pot preparation of the 4-methoxy-2-(pyrrol-2-yl)furan from the 2-acetoacetyl-pyrrole and coupling reactions of the C 5 -position of the 4-methoxy-2-(pyirol-2-yl)furan with various types of aldehydes and ketones as key steps.

Electro-initiated oxygenation of alkenylsilanes in the presence of thiophenol.

Abstract Electrolysis of alkenylsilanes in the presence of thiophenol with bubbling of molecular oxygen gave the corresponding α-phenylthio carbonyl compounds with the consumption of a catalytic amount of electricity. An electro-initiated radical chain mechanism is proposed. The reaction also took place without electrochemical initiation, but much longer reaction time was required for the completion of the reaction. Since various types of alkenylsilanes are prepared by the alkylation of 1-bromo-1-(trimethylsilyl)ethene, 1-bromo-1-(trimethylsilyl)ethene can be utilized as a synthon of phenylthioacetyl anion. The oxygenation of 1-phenylthio-1-(trimethylsilyl)alkenes in the presence of thiophenol gave α-phenylthio thiolesters indicating that the carbon-silicon bond was cleaved exclusively without affecting the carbon-sulfur bond.

Regiospecific conversion of alkenyl sulphides to α-sulphenylated carbonyl compounds by oxygenation in the presence of thiophenol

Regiospecific conversion of alkenyl sulphides to α-sulphenylated carbonyl compounds was achieved by oxygenation in the presence of thiophenol; electrolysis was found to be quite effective for initiation of the reaction.

Radical carbonylation of alkynes in the presence of thiols

Treatment of alkynes with thiols under an atmosphere of carbon monoxide initiated by azobis(isobutyronitrile)(AIBN) gives β-alkylthio-α,β-unsaturated aldehydes.