Thiophene 3- -4,5-dihydro

Tetrahydro-thiophen-l,l-dioxidc werden als Anionen von Lithiumalanat unter Ringverengung zu Cyclo-butenen reduziert3. 3,4-Dihydro-thiophen-1,1 -dioxide liefern dagegen offenkettige Diene4. 

The corresponding photocyclization of S-arylvinyl sulfides to dihydro-thiophens has been shown to proceed via short-lived thiocarbonyl ylide intermediates, formed in turn by cyclization of triplet excited states. 1-Phenylthio-3,4-dihydronaphthalene (49), for example, affords the colored thiocarbonyl ylide (50)44 the isolated products are derived by processes involving hydrogen abstraction and migration. The greater efficiency of the photocyclization of 2-thioaryloxyenones (51) to dihydrothiophens (52) has been attributed to the additional stabilization afforded to the ylide (53) by the carbonyl group.45 Other similar photocyclizations have been reported.46... 

Figure 8 outlines possible routes leading to cysteine specific products via 1-deoxypentosone. Under the chosen reaction conditions, (180 °C H-O) norfuraneol is further transformed via 4-hydroxy-5-metnyl-3-(2H)-thiophenone and 2-methyl-3-(2H)-thiophenone, into 2-methyl-3-mercapto-thiophene and 2-methylthiophene, respectively. Norfuraneol is a methylene active compound, which undergoes aldolcondensation with carbonyls forming colored nonvolatile products. 2-Mercaptopropionic acid may be formed from the mercaptoketone by oxidative cleavage. By this route 2-methyl-3-thiolanone and 2-methyl-4,5-dihydro-thiophene may result. 

The role of the zwitterion intermediate 164 and its rearrangement in the photocyclization of aromatic thioethers 163 to arene dihydro thiophene derivatives 165 is supported [81] by its independent trapping (via 1,3-dipolar cycloaddition) with biphenyl maleimide to obtain 166 in high yields (Scheme 8.47). 

Methyl-2,5-dihydro-thiophen-l,l-dioxid laBt sich in waBrig, alkalischem Medium photochemisch zu 3-Mcthyl-4,5-dihydro-thiophen-l,l-dioxid umlagem6 ... 

Dihydro-thiophen-1,1-dioxid Benzophenon Accton Hg-Licht 25° 0 Cl 6,7-Dichlor-3-thia-bicyclo [3.2.0]hep-tan-6,7-di-carbonsaure,-anhydrid-3s3-dioxid 13-55 3... 

Schwefelmonoxid (aus 2,3-Diphenylthiiran-l-oxid) eignet sich zur Reduktion von Pyri-din-N-oxiden zu Pyridinen4. Chinolin-N-oxide werden entsprechend durch 2,5-Dihydro-thiophen-1,1-dioxid zu Chinolinen reduziert5. 

Hydroxy 3-oxo-2,5-bis-[3,4-dimethyl-phenyI]-tetrahydrothiophen-l,l-dioxid3 21,4 g (60 mMol) 4-Hy-droxy-3-oxo-2,5-bis-[3,4-dimethyl-phenyl]-2,3-dihydro-thiophen-I,l-dioxid in 75 ml Eisessig, 75 ml Athanol und 75 ml THF werden auf 5° gekiihlt. Man fligt 19,5 g (0,3 g-Atom) Zinkstaub zu. Die erst griingelbe Farbe wird... 

Hydroxy-3-oxo- 2,5-bis-[3,4-dimethyl-pheny]]-tetrahydro- -1,1-dioxid aus 3-Hydroxy-4-oxo-2,5-bis-[3,4-dimethyl-phenyl]-4,5-dihydro-thiophen- 1,1-dioxid durch Reduktion mit Zn 710... 

Miscellaneous Physical Properties. The microwave spectrum of 2,3-dihydro-thiophen shows the molecule to be puckered and to have a barrier to inversion of 328 cm The non-planarity of 2-oxotetrahydrothiophen has been demonstrated by microwave spectroscopy. ... 

Dihydro thiophenes 1,3-dienes thiophenes. The salt reacts with a-mercap-to ketones to give dehydrothiophenes (1) in moderate yields (about 50-75%). 

Keto-thiols add to alkenylphosphonium ions, affording ylides which then ring close by Wittig reaction and give 2,5-dihydro thiophenes, which can be dehydrogenated. 

The x-ray crystallographic search for dihydrothiophenes revealed 42 hits. In most of the compounds, the thiophene ring was fused to a cyclic compound. X-ray studies of some dihydro thiophene-1,1-dioxides are also available. In most cases, the x-ray studies were used to determine the configurations of the substituents at the 2,3-position (i.e., cis or trans). 

Ary 1-4,5-dihydrothiophene-1,1-dioxides (38) imdergo base-catalyzed isomerization to 3-ary 1-2,5- (39) and 3-aryl-4,5-dihydrothiophene-l,1-dioxide (40) (Scheme 3). Although 2,5-dihydro-thiophene-1,1-dioxide is more stable than its 4,5-isomer, the presence of a substituent at the position, shifts the equilibrium to the right <80T1667>. 

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