Allylic Sulfides and Selenides

Alkyl and allyl sulfides and selenides can be transformed readily into the corresponding alkyl and alkenyl halides respectively. This reaction takes advantage of the easy formation of the corresponding sul-fonium and selenonium salts on reaction with alkyl halides, alkyl bromoacetates or bromine - (Scheme S3). A related process involves the intermediary formation of a selenoxide and its further reaction with hydrochloric or hydrobromic acids. ... 

Diorganochakogenides. A method for synthesis of allyl sulfides and selenides involves formation of allylsamarium bromide and its reaction with PhX-XPh (X=S, Se) in THF. For a similar approach to benzyl sulfides, the benzylsamarium halides are formed in the presence of BiClj. Aqueous media can be used in this latter reaction. 

Oxidative addition of allyl sulfides and selenides to Pd(0) complexes is a reversible process. The equilibrium is shifted to the 7/ -allylic dimer when Pd2(dba)3 is used (Equation (40)). ... 

As has been described for allyl bromide (see preceding paragraph), allyl sulfides and allyl phenyl selenide react with 6-diazopenicillanates 134 under Cu(acac)2 catalysis to give the products of ylide formation and subsequent [2,3] rearrangement 155-159). Both C-6 epimers are formed. The yields are better than with BF3 Et20 catalysis, and, in contrast to the Lewis acid case, no 6[Pg.139]

Lithiated allyl sulfides (in common with allyl sulfoxides and selenides, but in contrast with allyl ethers and allyl amine derivatives) tend to react with alkyl halides at the a position, adjacent to S.1 The best a-selectivities are obtained with lithium-coordinating S-substituents such as pyridyl (114),85 imidazolyl (115), and dimethylaminocarbonyl (116).1... 

Ketene, dichloroketene, and related compounds react with allylic ethers, sulfides, and selenides in a [3.3] sigmatropic rearrangement. This interesting reaction allows the synthesis of a number of medium and large ring compounds by expansion [72] [73] [74]. Dichloroketene has been prepared in situ by slow addi-... 

Ketene Claisen rearrangement. Dichlorokelene (1) reacts with the allylic sulfide 2 to give the expected [2 + 2] cycloadduct (3) and the S-phenyl ester of the unsaturated acid (4). The latter product is evidently formed by a Claisen rearrangement of a 1,3-dipolar intermediate (a). Products related to 4 are also obtained from allylic ethers and selenides in fact, in the case of allylic ethers only the rearranged esters are usually isolable. 

Competing reactions to addition to a-hetero-substituted alkenes are metallation of vinylic or allylic protons (see 5.5.2.3.2) and cleavage of the carbon-hetero-element bond (see 5.5.2.2.1.). a-Metallations occur with vinylic chlorides, fluorides and ethers no addition of RLi occurs with vinyl fluorides, chlorides or ethers. For vinylic sulfides and selenides, whether metallation or addition (or even carbon-heterobond cleavage) occurs depends on the conditions and reagents. Addition of RLi (R = Et or n-Bu, not Ph) occurs to aryl vinyl sulfides ... 

Transformations cf sulfides and selenides to organic halides the haloalkylation and halopropenylation of alkyl and allyl halides... 

Propargylic sulfides " and selenides have been metallated with n-butyllithium and lithium amide respectively, and allylated or alkylated selectively at the propargylic position (Scheme 34) with primary and secondary alkyl halides. - ... 

Phenyl propargyl sulfide " and selenide are rapidly deprotonated by 2 equiv. of base. The resulting dilithio derivatives react at their allylic rather than at their alkynic carbon centers (Scheme 34, entries c and d). Reduction of the sulfides allows the synthesis of 1,5-enynes (Scheme 34, entry b), whereas oxidation of the selenides leads to a-phenylseleno-a,P-unsaturated carbonyl compounds (Scheme 34, entry... 

Alkyl, benzyl, allyl and propargyl sulfides and selenides arising from the alkylation of the corresponding heterosubstituted organometallics have been used in several interesting transformations. These transformations take advantage of the easy reduction of the C—S and of the C—Se bond which can be carried... 

These reactions, coupl with the alkylations of sulfides and selenides, allow the homologation of primary alkyl halides - - - and the transformation of allyl halides to homoallyl halides. A related process, employing 2-methylthio- and 2-allylthio-thiazoline, allows the iodomeAylation (ICH2—) and the iodopropenylation (ICH2CH=CH—) of alkyl halides (Scheme 54).i3iii,i32.i7i... 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

Carbenoid attack at the heteroatom of allylic halides, ethers, amines, sulfides, and selenides generates an allylic ylide 23 that can undergo [2,3] sigmatropic rearrangement and, less frequently, [1,2] insertion (C-X insertion with and without allylic rearrangement, respectively). Similarly, an Af-acyl-2,5-dihydropyrrole could be cyclopropanated with ethyl diazoacetate in good yield. 

The BiBrs-Sm binary reagent promotes reductive C-S and C-Se bond formation between benzyl and allyl bromides and diorganyl disulfides and diselenides in aqueous media, affording the corresponding sulfides and selenides, respectively (Scheme 14.105) [217, 218]. Intramolecular reductive C-S bond formation by use of a BiCl3-M (M = Sn, Zn) redox system is used in the synthesis of 3-hydroxyceph-ems and 2-exo-methylenepenams (Scheme 14.106) [219]. Alkyl and arylsulfonyl chlorides couple with allylic halides in the presence of Bi to afford the corresponding allylic sulfones [220]. 

Allyl ethers, sulfides and selenides can react with dichloroketene to yield a.a -dichloro-y,<5-un-saturated esters together with cyclobutanones as byproducts25. Dichloroketene is prepared in situ by dehalogenation of trichloroacetyl chloride with zinc dust in absolute diethyl ether. The rearrangement usually proceeds at 25-30°C. 

Sulfides and selenides both stabilize an a-carbanion (see Section 1.1.5.2) and alkylation followed by elimination provides a route to substituted alkenes. Some examples of selenoxide eliminations are given in Schemes 2.24—2.26. Like the other syn eliminations described in this section, the regioselectivity of selenoxide elimination can be poor. Elimination normally takes place preferentially towards a conjugating (3-substituent or away from an electronegative p-substituent. This latter facet allows a good method for converting epoxides into allylic alcohols. 

Competitive experiments of allyl phenyl sulfide and allyl phenyl selenide with this system indicate that oxidative addition of the organic selenide is faster. The equilibrium displacement between the allylic sulfide and 7 -allylic complex depends on the actual precursor for Pd(0) phosphine complexes (Equation (41)). The stereochemistry of the reverse reaction on 7/ -cyclohexenyl palladium thiolate dimers (nucleophilic attack of sulfide) has been determined to be trans. According to the principle of microscopic reversibility, the oxidative addition of allylic sulfides must occur with inversion of configuration. 

LiBHEt3 has been found to reduce allylic ethers, caxboxylates, sulfides, sulfones, selenides and silyl ethers (equations 95 and 96).291... 

Allylation of a-thio-35), a-seleno-35) and a-silyl- 35,77) cyclopropyllithiums was not very successful35) but addition at —78 °C of 0.5 equivalent of copper (I) iodide-dimethylsulfide complex 35,106, W7> prior to the allylhalide leads 35,106,107) to a very high yield of homoallyl cyclopropyl sulfides or selenides (Scheme 24). Similar observations have been made on cyclobutyl derivatives3S). It is not clear at present whether a cuprate is involved in the process but we have evidence ( Se-NMR) that a new species is transiently being formed, at least in the seleno series. The synthesis of homoallyl cyclopropylsilanes was also reported 78) and involves the allylation of a postulated cuprate formed by the addition of lithium dibutyl cuprate to a-lithiocyclopropylsilane (Scheme 26). 

Whereas free singlet carbenes are rather unselective with respect to formation of cyclopropane 22 or ylide 23 and the cyclopropane is favored under conditions that populate the triplet state of a carbene (see Section I.2.I.2.4.2.6.2.), the metal carbenes generated with copper or rhodium catalysts display a selectivity for functional groups which are more nucleophilic than a double bond. Thus, no cyclopropanes are obtained from dialkylallylamines allyl sulfides -allyl dithioacetals , and allyl selenides under carbenoid conditions (copper or rhodium catalysts). 

Driven by the inability to substitute allyltin compounds at the 3-position, Keck examined intermolecular addition reactions of allyl sulfides [50]. He was able to show that 3-methyl- and 3,3-dimethyl-substituted allyl phenyl sulfides 86 and 88 undergo reaction with alkyl halides and alkyl phenyl selenides in the presence of hexabutylditin to form good yields of the allylation products (Scheme 18). These... 

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