Vinylsulfides

Reactions of sulfoxides containing a- and /9-hydrogen atoms, for example n-dibutyl sulfoxide 1170, with trimethylsilyl iodide 17 in the presence of tertiary amines such as diisopropylethylamine (DIPEA) give, e.g., the vinylsulfide 1171 as an 1 1 E/Z mixture in 75% yield and HMDSO 7 [16] (Scheme 8.4). Analogously, the vinyl sulfoxide 1172 or the vinyl sulfoxide 1174 furnish the 1,3-dienyl sulfides 1173 and 1175 in 91 and 85% yield, respectively, and HMDSO 7 [16]. 

Thioacetals eliminate to vinylsulfides in the presence of CuOTf (Scheme 46).192 Cu1 and Cu11 triflates are mild Lewis acids for Friedel-Crafts acylation and alkylation reactions. CuOTf effectively catalyzes the reaction of anisole with selenoesters.193,194 Copper(II) sulfate promotes epoxide ring opening reactions in the presence of pyridine,195 with retention of configuration being observed. Cu(OTf)2 is a catalyst for the ring opening of aziridine by aniline.196... 

Chloroethyl Methyl 1-Chloroacetamide 2-Chloroethyl Vinylsulfide 2-Chloroethyl Vinylsulfone 2-Chloroethyl Vinylsulfoxide 2-Chloroethylchloromethyl Sulfide [(2-Chloroethyl)sulfonyl]ethene 2-Chloroethylthio Ethene 2-(Chloromethyl)-l-propene 2-Chloro-/V-(2-chloroethyl)-N-methylacetamide 2-Ch loro-/V,/V-dimethy lam inoethane 2-Chloro-N,N-dimethylethanamine 2-Chloro-N,N-d imethylethylamine... 

Among the electron-rich alkenes, vinylsulfides are especially amenable to cation-radical reduction an important feature is the absence of hydrogenolysis of carbon-sulfur bonds. The reduction of [(phenylthio)methylene]cyclohexane is efficient (88%), and the retention of the phenylthio group clearly contrasts with catalytic hydrogenation (Mirafzal et al. 1993). This provides versatile functionality for further synthetic operations. 

Radical cyclization is an effective approach to the synthesis of isoquinolines (Scheme 8). In some cases these offer an alternative to the palladium-catalyzed reactions with aryl halide intermediates <99EJOC1925, 99TL1125>. For example, the radical cyclization of the iodide 37 onto the vinylsulfide moiety was followed by a cascade cyclization to form the benzo[n]quinolizidine system <99TL1149>. In some cases the radical cyclization can take place without the need for a halo intermediate. The reactive intermediate of 38 was formed on the nitrogen as an amidyl radical, which underwent tandem cyclizations to the lycorane system <99TL2125, 99SL441>. 

A radical cyclization controlled by sulfur yields the tetrahydroisoquinoline (Equation 49) <1997J(P1)2291>. In the absence of the sulfur groups, only the reduced product is isolated. Further reactions that utilize radical cyclizations with vinylsulfides show a cascade reaction eventually forming the benzo[ ]quinolizine system <1999TL1149> (Equation 50). 

Michael addition of pentM-yn-1-thiol to an activated alkyne produces co-yne vinylsulfides 424 as a separable mixture of the E and Z isomers. On treatment with -Uu (SnI I and a radical initiator, these substrates undergo a double radical cyclization accompanied by [(-fragmentation of the stannyl radical. The process is regio-, chemo-, and stereo-selective and produces the -isomer of the 5-substituted 3,4-dihydm-2//-thiopyran (Scheme 134) <1997JOC8630>. 

In combination with the range of standard transformations of alcohols, alkenes, and vinylsulfides, these silicon-tethered additions of functionalized radicals offer a versatile and stereoselective approach to amino alcohol synthesis. Whereas vinyl and 2-oxoethyl radicals have not yet been demonstrated as competent participants in the various intermolecular additions reported in the literature, the temporary tether approach allows such functionalized fragments to be installed in an efficient and stereoselective manner. Synthesis of the aminosugar daunosamine from achiral precursors shows how this concept, employing hydrazone radical acceptors, can be merged with asymmetric catalysis to achieve practical synthetic advances. 

Reductive lithiation of the vinylsulfide 67 derived from a cyclic ketone provides a valuable alternative to the Shapiro reaction (section 8.1),84 and the sequence of events leading to 68 or 69 determines the regioselectivity. 

Should added unsaturation be desired, the condensation of a 2-cyclopentenone with lithio cyclopropylphenyl sulfide makes possible the formation of an ally lie alcohol which can be dehydrated quantitatively (Scheme 11). Thermal rearrangement, followed by mercuric ion-promoted hydrolysis of the vinylsulfide part structure completes the synthetic transformation. 

A second metal-catalyzed route to alpha-thioboronate esters consists of the regiospecific, Markovnikov hydroboration of phenyl vinylsulfide which proceeds in high yield to give 14a,b (Equation 11). We are in the process of extending this unique reaction to other alkenyl sulfides and to alkenyl phosphines in order to determin whether the observed regiochemistry of addition is due to a directing effect of the soft heteroatom donor towards the catalyst center. 

Diboration of phenyl vinylsulfide to give 15 is best performed with a phosphine-free Pt catalyst, as Wilkinson s catalyst affords the Z-(phenylthio)-vinylboronate ester side product, 16, presumably due to (3-hydrogen elimination being competitive with B-C reductive elimination (Equation 12). 

Aryl ethers were also coupled intramolecularly with enol ethers when vinylsulfide was used as initiator of the coupling reaction the selectivity could be improved considerably [172e]. Additionally, the coupling to furan rings was studied, which led to advanced intermediates for the synthesis of bicyclic furan-containing natural products [172e],... 

Syntheses of heterocycles from fluorinated vinylsulfides 03UK394. 

The a-alkylation of sulfonylhydrazone dianions with disulfides followed by Shapiro reaction has been used to effect the 1,2-transposition of carbonyl groups.19,20 As shown below, treatment of tosylhydrazone 31 with n-BuLi/TMEDA followed by addition of dimethyl disulfide and deprotonation with an additional equivalent of w-BuLi provided vinylsulfide 32.19 Exposure of this compound to mercuric chloride in hot aqueous acetonitrile provided ketone 33 in 75% overall yield. 

Kovregin, A.N. Sizov, A.Y Ermolov, A.R Synthesis of substituted thiophenes based on fluoro-containing vinylsulfides. Izv. Akad. Nauk, Ser. Khim. 2002, 6, 945-947. 

Uber die Ylidstufe (107) scheint die Fragmentierung von S-Methyl-thiolanium-jodid mit Phenyl-lithium zu Athylen und Methyl-vinylsulfid zu verlaufen (99). 

An interesting application of the chiral cyclopalladated complexes is palladium-promoted asymmetric Diels-Alder reactions of l-phenyl-3,4-dimethylphosphole (Scheme 4). In the original report on the Diels-Alder reaction of the phosphole reported by Nelson and co-workers, the dichloropalladium species was employed as a promoter.f In 1994, Leung showed that a chiral cyclopalladated complex was capable of promoting the Diels-Alder reaction. In this reaction, the chiral palladacycle worked as a chiral auxihary and showed almost perfect diastereoselectivity. It has been revealed that simultaneous precoordination of a diene and a dienophile to the palladium center is essential for the reaction. Thus, both dienes and dienophiles should possess Lewis basic functionahty. The diene l-phenyl-3,4-dimethylphosphole has been the only substrate examined so far, while a variety of dienophiles, such as vinylphosphine, vinyl-sulfoxide, vinylsulfide, acrylamide, vinylarsine, vinylpyridine, vinyl-pyrrole, or methylenequinuchdinone, have successfully been applied to this asymmetric Diels-Alder reaction. 

Mo(CH-r-Bu)(NAr)(OR)2 with vinylethers or vinylsulfides, so perhaps rhenium complexes are inherently more tolerant of functional oups directly attached to the alkylidene a carbon atom, a proposal that would be consistent with the observed greater tolerance of classical heterogeneous Re catalysts toward functional groups. ... 

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