Tetrahydrothiophen Compounds

The (+)-biotin precursor (13) has been conveniently prepared from 

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Among the widely studied [AuX(PR3)] (X = halogen, PR3 tertiary phosphine) [AuBrL] (L = 2-methylphenylphosphine) crystallizes as a folded chain [65]. Chains of the tetrahydrothiophene and tetrahydroselenophene complexes [AuX(EC4H8)] (E = S, X = Cl, Br or I E = Se, X = I) [66, 67] exhibit different patterns. In the crystal structure of the tetrahydrothiophene compounds [AuX(SC4H8)] (X = Cl, Br) neutral units associate, whereas the structure of the iodine complexes consists of Aul2 and... 

Properties. Sulfolane [126-33-0] C4HgS02 (1), also known as tetrahydrothiophene-1,1-dioxide and tetramethylene sulfone, is a colorless, highly polar, water-soluble compound. Physical properties are given ia Table 1 (1). 

Thiophene is the typical model compound, which has been extensively studied for typifying gasoline HDS. Although, some results are not completely understood, a reaction network has been proposed by Van Parijs and Froment, to explain their own results, which were obtained in a comprehensive set of conditions. In this network, thiophene is hydrodesulfurized to give a mixture of -butenes, followed by further hydrogenation to butane. On the considered reaction conditions, tetrahydrothiophene and butadiene were not observed [43], The consistency between the functional forms of the rate equations for the HDS of benzothiophene and thiophene, based on the dissociative adsorption of hydrogen, were identical [43,44], suggesting equivalent mechanisms. 

This technique has been applied to the determination of aromatic hydrocarbons, alcohols, aldehydes, ketones, chloroaliphatic compounds, haloaromatic compounds, acrylonitrile, acetonitrile, mixtures of organic compounds and tetrahydrothiophene in soils, chloroaliphatic and haloaromatic compounds and organotin compounds in non-saline sediments, and organotin compounds in saline sediments. 

The overall structural motif of pure organocopper compounds can be changed dramatically by the addition or the presence of coordinating solvents such as DMS or THT (THT = tetrahydrothiophene). This is illustrated by comparison of the structures of [Cu4Mesityl4(THT)2], and [CusMesityh] (see Fig. 1.8) [63, 64]. 

Treatment of 77 with one equivalent of [AuCl(tht)] (tht = tetrahydrothiophene) leads to the type III AuCl bridged pincer complex 79 in high yield (counterion is Cl ) [149]. The unique complex 79 is the only heterodimetallic compound with two metal atoms attached at a carbodiphosphorane carbon(O) atom. The environment at the central carbon atom is planar in 77 and pyramidal in 78 and 79. P-C bond lengths and P-C-P angles in the dication 78 are closely related to those in the neutral Pt complex 36 (Fig. 25). The two metals of 79 attached to the carbon atom are coimected via a very short d -d ° pseudo closed shell interaction with a Pd-Au bond length of 2.8900(3) A a similar bonding situation (aurophilic attraction) is found in the gold complex 29 shown in Fig. 23. 

Numerous examples involving the preparation of tetrahydrothiophenes via [3 + 2] cycloaddition of thiocarbonyl ylides with electron-poor alkenes have been reported. Thiobenzophenone (5)-methylide (16), generated from 2,5-dihydro-1,3,4-thiadiazole (15) and analogous compounds, react with maleic anhydride, N-substituted maleic imide, maleates, fumarates, and fumaronitrile at —45°C (28,91,93,98,128,129). Similar reactions with adamantanethione (5)-methylide (52) and 2,2,4,4-tetramethyl-3-thioxocyclobutanone (5)-methylide (69) occur at ca. +45°C and, generally, the products of type 70 were obtained in high yield (36,94,97,130) (Scheme 5.25). Reaction with ( )- and (Z)-configured dipolaro-philes stereospecifically afford trans and cis configured adducts. 

An attempted synthesis of biotin using thiocarbonyl ylide cycloaddition was carried out (131,133,134). The crucial step involves the formation of the tetrahydrothiophene ring by [3 + 2] cycloaddition of a properly substituted thiocarbonyl ylide with a maleic or fumaric acid derivative (Scheme 5.27). As precursors of the thiocarbonyl ylides, compounds 25a, 72, and 73 were used. Further conversion of cycloadducts 74 into biotin (75) required several additional steps including a Curtius rearrangement to replace the carboxylic groups at C(3) and C(4) by amino moieties. 

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