Yoshiaki Sugihara

The Chemistry of Thiophene 1-Oxides

Abstract An exhaustive literature survey has been made of the chemistry of thiophene 1-oxides (thio- phene S-oxides). Syntheses, structures, and reactions of thiophene 1-oxides are described to understand the present status of this chemistry. The chemistry of selenophene 1-oxides is also described briefly.

Chemistry of Thiophene 1,1-Dioxides

Thiophene oxides, where two pairs of lone pair electrons are consumed for bond formation with oxygen atoms, are no longer aromatic. Their chemistry has now grown into an important branch both in heteroatom and heterocyclic chemistry from synthetic, mechanistic, structural, and theoretical points of views. Thiophene 1,1-dioxides are most commonly prepared by oxidation of thiophenes. As unsaturated sulfones, they serve as dienophiles, 1,3-dipolarophiles, and Michael acceptors. They, as dienes, undergo a wide variety of synthetically useful Diels-Alder reactions and occasionally undergo even [4+6] cycloadditions. Many important reactions, which are not included in these categories, are also known. The present article describes the chemistry of thiophene 1,1-dioxides, with special emphasis being placed on their synthesis and synthetic applications. Many references on structural and theoretical studies are also given. The chemistry selenophene 1,1-dioxides is referred simply.

Synthesis and characterization of 3,4-dl-t-butylfuran, pyrrole, and selenophene

Abstract 3,4-Di-t-butylfuran ( 1 ), pyrrole ( 2 ), and selenophene ( 4 ) were first synthesized using 3,4-di-t-butylthiophene ( 3 ) as the starting material and these overcrowded five-membered hetarenes including 3 were characterized by NMR and MMP 2 calculations.

1-IMINO AND 1,1-DIIMINO DERIVATIVES OF 3,4-DI-TERT-BUTYLTHIOPHENE

Abstract The reaction of 3,4-di-tert-butylthiophene (2) with N-[(p-tolylsulfonyl)imino]-phenyliodinane (TsN=IPh) in the presence of Cu(MeCN)4PF6 in MeCN at room temperature provided 3,4-di-tert-butyl-1-[(p-tolylsulfonyl)imino]-1,1-dihydrothiophene (3), 3,4-di-tert-butyl-1,1-bis[(p-tolylsulfonyl)imino]-1,1-dihydrothiophene (4), and 1-(p-tolylsulfonyl)-3,4-di-tert-butylpyrrole (5) as the principal products. The use of 2 in a large excess gave 3 in a better yield of 61%. Results of the X-ray crystallographic analyses of 3 and 4 are also reported.

SYNTHESIS OF SULFUR-CONTAINING LARGE-MEMBERED HETEROCYCLES (CROWN THIOETHERS) WITH BIS(O-MERCAPTO)PHENYL SULFIDE

Abstract Bis( o -mercaptophenyl) sulfide ( 4 ) condensed with 1,2-dibromoethane in the presence of Cs 2 CO 3 in DMF to give the 9-membered-ring 1:1-condensation product ( 9 ), the 18-membered ring 2:2 condensation product ( 10 ), and the 27-membered ring 3:3 condensation product ( 11 ) in 42, 19, and 5% yields, respectively. The condensation of 4 with 1,3-dibromopropane gave the 10-membered ring 1:1 condensation product ( 12 ) as the sole identifiable product in 42% yield. The reaction of 4 with cis -1,2-dichloroethylene in refluxing EtOH in the presence of EtONa provided the two isomeric 1:1-condensation products ( 14 ) (25%) and ( 15 ) (5%) along with the 2:2 condensation product ( 16 ) (20%). X-Ray crystallographic analyses of 10, 14 , and 15 are also reported.

π-Face-selective hetero Diels-Alder reactions of 3,4-di-tert-butylthiophene 1-oxide. An excellent trapping reagent for thioaldehydes and thioketones

Hetero Diels–Alder reactions of 3,4-di- tert -butylthiophene 1-oxide ( 1 ) with thioaldehydes and thioketones take place exclusively, except the reaction with thiobenzophenone, at the syn -π-face of 1 with respect to the SO bond. The π-face selectivity was explained in terms of the extent of conformational changes of 1 that are brought about in the process to the transition states.

Stereoisomerism based on high-energy inversion barrier of pentathiepane ring: Preparation and isolation of conformers

Abstract Sulfuration of acenaphtho[1,2-a]acenaphthylene (1) with elemental sulfur gave a pentathiepane derivative (2). Dynamic NMR analyses revealed that the two naphthalene rings of 2 are chemically nonequivalent up to 100 °C due to freezing of the inversion of the pentathiepane ring. Thus, sulfuration of 5-phenylacenaphtho[1,2-a]acenaphthylene gave a pair of conformers which were isolable and whose steterochemistry was determined by X-ray diffraction analysis. These conformers isomerized slowly to each other in solution at room temperature.

Reactions of acetylenes, possessing bulky alkyl substituents, with S2Cl2. Unexpected formation of α-oxothioketones, thiirene 1-oxides, and 1,2-dithietes

Abstract The reaction of di-t-butylacetylene with S2Cl2, followed by purification with silica-gel column chromatography, gave 2,2,5,5-tetramethyl-4-oxo-3-hexanethione (4a) (37%) and 2,3-di-t-butylthiirene 1-oxide (5a) (10%), which were formed by hydrolysis of the initial product, 2,3-di-t-butyl-2,3-dichloroepisulfide (3a). The same work-up of the reaction mixture of di(1-adamantyl)acetylene with S2Cl2 provided 2-oxoethanethione (4b) (4–33%), thiirene 1-oxide (5b) (8–27%) and 1,2-dithiete (9b) (3–21%). The reaction of 2,2,5,5,6,6,9,9-octamethyl-3,7-decadiyne (1c) with S2Cl2 furnished a 4H,5H-thiepin (12) as the sole product in 99% yield.

Thiophene sulfoximides: 2,4- and 3,4-di-tert-butyl-1-imino-1,1-dihydrothiophene 1-oxides

Preparation of sulfoximide derivatives of monocyclic thiophenes is reported. Treatment of 2,4-di- tert -butylthiophene 1-oxide ( 4 ) with N -[( p -toluenesulfonyl)imino]-phenyliodinane (TsN=IPh) in the presence of Cu(MeCN) 4 PF 6 in MeCN at room temperature provided 2,4-di- tert -butyl-1-[( p -toluenesulfonyl)imino]-1,1-dihydrothiophene 1-oxide ( 8 ) in 81% yield. Hydrolysis of 8 with concentrated H 2 SO 4 at room temperature furnished 2,4-di- tert -butyl-1-imino-1,1-dihydrothiophene 1-oxide ( 9 ) in 89% yield. Optical resolution of a pair of enantiomers of 9 was performed by HPLC on a chiral column and their absolute configuration was determined by an X-ray crystallographic analysis.

A new route to dithiirane 1-oxides: Oxidation of tetrathiolanes with dimethyldioxirane

Oxidation of di-1-adamantyltetrathiolane with dimethyldioxirane (DMD) in dichloromethane and acetone gave di-1-adamantyldithiirane 1-oxide. Similarly, reaction of 1-adamantyl- t -butyltetrathiolane with DMD gave (1 RS ,3 SR )- and (1 RS ,3 RS )-1-adamantyl- t -butyldithiirane 1-oxides. In the reactions, intermediary formation of tetrathiolane 1-oxides was suggested by low-temperature 13 C NMR.