Vinyl thioethers groups with

The hydrothiolation of terminal alkyl alkynes with 96 (Fig. 2.17) proceeds with good degree of regio- and chemo-selectivity, especially with thiophenol and p-methoxy-thiophenol as substrates. Isomerisation to the internal alkenyl thiolates accounts for less than 9% of the thiolated products under the reaction conditions. In addition, further hydrothiolation of the vinyl thioether product is not observed. Typical conversions of 70-85% at 1 mol% loading at 80°C within 5 h are observed. Arylthiols substituted with electron-withdrawing groups afford lower conversions. 

A recently developed application of the Ramberg-Backlund reaction is the synthesis of C-glycosides. The required thioethers can be prepared easily by exchange with a thiol. The application of the Ramberg-Backlund conditions then leads to an exocyclic vinyl ether that can be reduced to the C-nucleoside.95 Entries 3 and 4 in Scheme 10.6 are examples. The vinyl ether group can also be transformed in other ways. In the synthesis of partial structures of the antibiotic altromycin, the vinyl ether product was subjected to diastereoselective hydroboration. 

For the addition of ethylene, EtOAc as solvent was particularly advantageous and gave 418 in 60% yield (Scheme 6.86). The monosubstituted ethylenes 1-hexene, vinylcyclohexane, allyltrimethylsilane, allyl alcohol, ethyl vinyl ether, vinyl acetate and N-vinyl-2-pyrrolidone furnished [2 + 2]-cycloadducts of the type 419 in yields of 54—100%. Mixtures of [2 + 2]-cycloadducts of the types 419 and 420 were formed with vinylcyclopropane, styrene and derivatives substituted at the phenyl group, acrylonitrile, methyl acrylate and phenyl vinyl thioether (yields of 56-76%), in which the diastereomers 419 predominated up to a ratio of 2.5 1 except in the case of the styrenes, where this ratio was 1 1. The Hammett p value for the addition of the styrenes to 417 turned out to be -0.54, suggesting that there is little charge separation in the transition state [155]. In the case of 6, the p value was determined as +0.79 (see Section 6.3.1) and indicates a slight polarization in the opposite direction. This astounding variety of substrates for 417 is contrasted by only a few monosubstituted ethylenes whose addition products with 417 could not be observed or were formed in only small amounts phenyl vinyl ether, vinyl bromide, (perfluorobutyl)-ethylene, phenyl vinyl sulfoxide and sulfone, methyl vinyl ketone and the vinylpyri-dines. 

Thio-ene addition is another attractive method for the attachment of organic thioether groups to polysiloxane chains. It is based on the free-radical addition of a thiol group to a vinyl-substituted siloxane or the addition of a terminal alkene to a thiol-substituted siloxane (Eq. 2). " Boileau et al. used this reaction to graft different amino acids to the polymer backbone to induce potential interactions with polar surfaces. 

The relative ease of the cyclization step from A to C may also be linked to the nucleophilic or coordinative ability of the heteroatom bound to the metal. The reaction of 7 with diphenylacetylene (Ph2C2) leads to the seven-membered derivatives 68 and 69 after prior isolation of the monoinsertion product 24, treatment with a silver salt, followed by the usual thermolytic conditions. This is another rare example of an intramolecular formation of a C-S bond within the coordination sphere of a transition metal and a novel, albeit limited to one alkyne, route to the rare family of dibenzo[bd] thiepins. With the closely related 8, which differs from 7 only by the tertiary amine unit in the metallacyclic framework instead of a thioether function, a carbocyclic product 71 is obtained (see under carbocycle reactions, next section). The formation of the seven-membered S-heterocycles is attributed to the good coordinative ability of the thioether group in 7. The S-atom remains close to the vinylic carbon function before the cyclization. With the poorly coordinating, readily displaced amine function in 8, the N-atom is detached from the metal and ultimately affords a spirocyclic product (see Scheme 18). 

In 2013, Lei s group described an elegant methodology that utilizes the in situ formation of o-quinolinone quinone methide from suitable precursor under physiological conditions. The in situ-generated methide reacts with vinyl thioethers as electron rich dienophile in hetero-Diels-Alder reaction. This chemistry was successfully used for live cell imaging [78]. 

Isolated cytochrome c in neutral solution shows absorption bands at 408, 530, and 695 m/x in the oxidized form and at 415, 520, and 550 m/x in the reduced form. The heme group is not readily removed by treatment with acid acetone. Following hydrolysis with hydrochloric acid a porphyrin can be isolated which is referred to as porphyrin c. This porphyrin differs from protoporphyrin IX in the nature of side chains 2 and 4 in which the vinyl groups are replaced by thioether bridges with cysteine (Fig. 10). 

This hypothesis has been verified starting from (Z)-y-iodoallyl ethers [109], amines [107], and thioethers [107] (Scheme 7-95) that are easily accessible from a propargyl ether [110] or ethyl propiolate [111]. In each case, the heteroatom chelates the vinylmetal to form a rigid five-membered ring and the allyl moiety approaches the vinyl one with a diastereofacial selectivity anti to the alkyl group [112]. 

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