Allyl thioethers

Anions of allylic thioethers may also be alkylated with alkyl bromides in high yield. The thioether groups can subsequently be removed by hydrogenolysis (F.W. Sum, 1979). 

The reaction of the thiolated PVC with Chloramine T carried out and the structure ( ) of the resultant polymer was examined (1 ). In the case of phenyl-thioether, the sulfilimine structure (2) was mainly produced accompanied with, in part, the sulfenamide structure (8,) binded to the main chain with N atom, the case of allyl thioether derivative containing C=C moiety in the pendent group, the sulfilimine (9) formed rearranged exclusively in Claisen type to the sulfenamide structure (10) connected to the main chain with S atom. 

Haloarene chromium tricarbonyl complexes are activated to nucleophilic attack by thiolate anions [58, 59]. High yields of the thioethers are obtained under liquiddiquid two-phase conditions, but optimum yields are achieved under soliddiquid conditions. In many cases the thioether is produced directly but, where the reaction mixture contains thioether and its chromium complex, the thioether can be isolated by degradation of the complex with iodine or an excess of the thiol. Both 1,2- and 1,4-dichlorobenzenes yield only monothioethers, even when an excess of thiolate anion is used. In contrast, 1,3-dichlorobenzenes produce a mixture of the mono- and dithioethers [59]. Aryl allyl thioethers have been produced under catalysed Heck reaction conditions from S-allyl thiocarbamates and iodobenzene [60]. 

If olehn metathesis is to be conducted in solution, solvents of low Lewis-basicity will generally give the best results (CH2CI2 > toluene > THF). As discussed above, metathesis is initiated by the formation of a jt-complex between the metal and the alkene. Hence, other nucleophiles will compete with the alkene for these coordination sites and in some systems even THF can lead to complete deactivation of the catalyst [786]. Tungsten-based catalysts which can even metathesize allyl thioethers have, however, been described [787]. 

In addition to 1,2-alkyl shifts, sulfonium ylides with P-hydrogen can also undergo fragmentation into an olefin and a thioether [1317,1318]. When allylic thioethers are treated with two equivalents of ethyl diazoacetate in the presence of a catalyst for diazodecomposition, S-alkylation and elimination of the thioalkyl group from the initially formed a-alkylthio-4-alkenoic esters occurs to yield 2,4-dienoic esters [1319]. 

The heterocyclic component in the leaving group offers possibilities for introduction of chirality. Optically active oxazolin-2-yl and thiazolin-2-yl allyl thioethers 7 were thus chosen as substrates (Scheme 8.8) [17]. 

Scheme 8.8. Enantioselective substitution of oxazolin-2-yl and thiazolin-2-yl allyl thioethers.

Allyl amines, allyl thioethers, and allylferrocenylselenide react analogously with butatrienylidene complex 10 by initial addition to C3 and subsequent hetero-Cope or hetero-Claisen rearrangement (Scheme 3.23) [21, 42-45]. 

Asymmetric induction has been reported for a ketene Claisen rearrangement of the adducts of dichloroketene to chiral allyl thioethers as a route to precursors of optically active y-butyrolactones [504], An example of this sigmatropic step is given hereafter. 

Methylidenation of allylic thioethers. Methylidenation of an allylic phenyl-thioether with methylene iodide-diethylzinc is accompanied by a 2,3-sigmatropic rearrangement to a homologous allylic phenylthioether. The rearrangement is also initiated by ethylidene iodide. Cyclopropanation is not observed. The Simmons-Smith reaction with allylic sulfides results only in formation of an insoluble polymer. 

An interesting Fe-catalyzed SN2 -like carbene insertion reaction using diazo compounds and allyl sulfides (the Doyle-Kirmse reaction) was reported by Carter and Van Vranken in 2000 [20], Various allyl thioethers were reacted with TMS-diazomethane in the presence of catalytic amounts of Fe(dppe)Cl2 to furnish the desired insertion products with moderate levels of stereocontrol [Equation (7.6), Scheme 7.14]. The products obtained serve as versatile synthons in organic chemistry, e.g. reductive desulfurization furnishes lithiated compounds that can be used in Peterson-type oleftnations to yield alkenes [Equation (7.7), Scheme 7.14] [21]. 

Moreover, trapping of the carbene (159, R = pTol) by an allyl thioether leads largely to (160) removal of the protecting group provides a simple route to artemesia ketone (161) in 65% yield from (156, R = pTol) 126) ... 

Treatment of the 2-pyrrolyl allyl thioether (498) with acetic anhydride and quinoline at 170 °C (or in A jV-dimethylaniline at ca. 100 °C) results in a thio-Claisen rearrangement to give the 5-(3-allyl-2-pyrrolyl) thioacetate (499), whilst peracid oxidation of (498) produces the non-rearranged sulfone in low yield and Raney nickel reduction of (498) yields 3-propylpyrrole (78CJC221). The polyphosphoric acid-catalyzed cyclization of (2-pyrrolylthio) acetic acid (501 R = R = H) somewhat unexpectedly yields (502) via the Spiro intermediate, instead of forming the expected oxothiolane (500), which can be obtained by a Dieckmann cyclization of ethyl (3-ethoxycarbonyl-2-pyrrolylthio) acetate (501 R = Et, R = C02Et) (B-77MI30506). 

Hydrolysis of the 2-thioethers is easily accomplished by acid treatment, but the ring collapses and the product is a mixture of the dialdehydes corresponding to maleic and fumaric acids.202 Heating 2-furyl allyl thioethers at only 70 C induces a thio-Claisen rearrangement to the 3-position as expected203 the reaction is first order with an activation energy of96 kJ/mol. 

Intramolecular cyclization to macrocyclic terpenoids. Treatment of the allylic thioether (1), prepared from rrans,fra 5-geranyllinalool, with n-butyl-lithium in THF at -78° in the presence of DABCO, leads to a carbanion that... 

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