Alkenyl sulfide

The thioboration of terminal alkynes with 9-(alkylthio)-9-borabicyclo[3.3.1]-nonanes (9-RS-9-BBN) proceeds regio- and stereoselectively by catalysis of Pd(Ph,P)4 to produce the 9-[(Z)-2-(alkylthio)-l-alkeny)]-9-BBN derivative 667 in high yields. The protonation of the product 667 with MeOH affords the Markownikov adduct 668 of thiol to 1-alkyne. One-pot synthesis of alkenyl sulfide derivatives 669 via the Pd-catalyzed thioboration-cross-coupling sequence is also possible. Another preparative method for alkenyl sulfides is the Pd-catalyzed cross-coupling of 9-alkyl-9-BBN with l-bromo-l-phe-nylthioethene or 2-bromo-l-phenylthio-l-alkene[534]. 

Aryl sulfides are prepared by the reaction of aryl halides with thiols and thiophenol in DMSO[675,676] or by the use of phase-transfer catalysis[677]. The alkenyl sulfide 803 is obtained by the reaction of lithium phenyl sulfide (802) with an alkenyl bromide[678]. 

Finally the new ylides stabilized with sulfinyl but alkoxy carbonyl groups also behave in a more complex manner than for the simple sulfinyl ylide and the loss of both PhjPO and PhjP is observed [131]. Mixtures of products are obtained among which are alkenyl sulfides as major products but also sulfides and thioesters (Scheme 35). 

Failure to achieve the bicyclization of diallyl ether with nBu2ZrCp2 led to the unexpected discovery of the oxidative addition reaction,226 shown in Scheme 44. This reaction has been extensively used for developing synthetically useful reactions, also shown in Scheme 44 232 234>234a-234c Another breakthrough on this topic was made with alkenyl chloride,235 which led to more recent similar discoveries with alkenyl sulfides, sulfones, and ethers236,23611 237 (Scheme 45). 

The Lewis acid catalyst 53 is now referred to as the Narasaka catalyst. This catalyst can be generated in situ from the reaction of dichlorodiisopropoxy-titanium and a diol chiral ligand derived from tartaric acid. This compound can also catalyze [2+2] cycloaddition reactions with high enantioselectivity. For example, as depicted in Scheme 5-20, in the reaction of alkenes bearing al-kylthio groups (ketene dithioacetals, alkenyl sulfides, and alkynyl sulfides) with electron-deficient olefins, the corresponding cyclobutane or methylenecyclobu-tene derivatives can be obtained in high enantiomeric excess.18... 

The iron-catalyzed cross-coupling between Grignard reagents and alkenyl sulfides was also studied (Scheme 26) . Unfortunately, this reaction is very sensitive to steric and electronic effects and only two products were synthesized in modest yields. In fact, the scope of the reaction is very limited since only vinyl sulfides can be used. 

Reaction of the alkenylmagnesium intermediates 184 with several electrophiles led to trisubstituted alkenyl sulfides 186 (Table 14). Thus, when the reaction was quenched with D2O, the deuteriated vinyl sulfide (186 E = D) was obtained in 80% yield with 98% deuterium incorporation. The reaction with aldehydes, benzoyl chloride and iodine gave moderate to good yields of the desired functionalized alkenyl sulfides (186) however, ethyl chloroformate did not give good result. 

Synthesis of alkenyl sulfides and ketenedithioacetals from thiolesters and dithiocarbonates... 

Another way of synthesis of ketencdithioacetals and of alkenyl sulfides makes use of an alkylidenation of dithiocarbonates or thiolesters with a reagent introduced by Takai [439] and prepared from R CHBr2, Zn, TiCl4 and TMEDA (Table 4.4). 

The terpenes used were mainly /3-pinene fractions provided by DRT (Soci6td des Derives Rdsiniques et Terpeniques, Vielle-S Girons) and, for certain experiments a turpentine oil containing the main three terpenes a-pinene, /3-pinene, and A -carene. The /3-pinene fractions contained 80-90% /3-pinene, 2% a-pinene, 4-5% myrcene, 2-3% dipentene and 700-1500 ppm S. GC-MS analyses showed that sulfur impurities were composed of alkyl and alkenyl sulfides (mainly dimethyl sulfide), alkyl and alkenyl disulfides (mainly dimethyl disulfide), trisulfides, thiophene and alkylthiophenes (methyl, dimethyl, acetyl and tertiobutyl). 

The asymmetric cross-coupling of zinc reagent 20 with ( )- and (Z)-l-bromo-2-(phenylthio)ethenes (23) catalyzed by Pd/(S)-(/ )-PPFA (10a) gave optically active alkenyl sulfides 24, which could be a potential substrate for the second cross-coupling, that is, the sulfide is replaced by the Grignard reagent in the presence of a nickel catalyst [26] (Scheme 8F.8). 

Alkenyl sulfides.6 An attractive route to vinyl sulfides involves cross coupling of a primary 9-alkyl-9-BBN with 1-bromo-l-phenylthioethene catalyzed by Pd(0) in the presence of a base, NaOH or K2HP04. This coupling can be extended to (E)- and... 

A detailed study of the halocyclisation of unsaturated benzyl sulfides has shown that tetrahydrothiopyran formation is favoured from alkenyl sulfides through 6-endo-trig and 6-exo-trig modes. However, for alkynyl sulfides only the 6-exo-dig cyclisation is predominant, leading to dihydrothiopyrans (95JOC6468). 

The halocyclization of unsaturated benzyl sulfides is influenced by the degree of unsaturation. Thus alkenyl sulfides yield tetrahydrothiopyrans through (y-endo-trig and (y-exo-trig modes (Equation 141), whereas alkynyl sulfides afford 2-methylenetetrahydrothiopyrans by a 6-exo-dig cyclization (Equation 142) <1995JOC6468>. 

The treatment of 7V-tosyl-/>-anisidine (75) and several of its derivatives with BTIB in the presence of activated alkenes provides an interesting example of an intermolecular cyclodehydrogenation sequence (99H1785). Arylpropenes are converted to 7V-tosylindolines 76 under these conditions, while alkenyl sulfides lead to the 7V-tosylindoles 77 (Scheme 22). The intermediate formation of 7V-tosylnitrenium ions in these reactions was suggested. 

Nucleophilic substitution of a,/3-epoxysilanes followed by the Peterson elimination is valuable for the stereoselective synthesis of alkenes.3 The reactions with lithium phenylsulfide and diphenylphosphide form alkenyl sulfides and alkenylphosphines, respectively, in a stereospecific manner. 7-Metallo-a,/ -epoxysilanes are isomerized to a-siloxyallylmetals by anionic ring opening and subsequent Brook rearrangement (Equation... 

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. 

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