Sulfinyl precursors

Pyrrolo[2,l-c][l,4]benzothiazepine 297 (R=Ph) has been prepared by an intramolecular nucleophilic displacement of acetyl derivative 296 (Scheme 64 (1992H51)). The same compound and its aryl (R = Ar (1992H51)) and carboethoxy or cyano (R = C(30Et or CN (1990H1291)) analogs can also be obtained by a Pummerer rearrangement-cyclization of sulfinyl precursor 298. 

Recently, a new synthetic route toward PPV and its derivatives has been reported in which the monomer is polymerized toward a dithiocarbamate precursor polymer by the additimi of a strong base. The corresponding conjugated polymer is obtained via a heart treatment of the precursor polymer. This dithiocarbamate precursor route represents a compromise between several straightforward but sometimes troublesome precursor routes and the more complex sulfinyl precursor route [134]. 

Vanderzande, DJ.M., Marin, G.B., 2011. Kinetic Monte Carlo modeling of the sulfinyl precursor route for poly (p-phenylene vinylene) synthesis. Macromolecules 44, 8716-8726. 

The sulfinyl precursor route is distinct from other radical/anionic polymerizations as the monomer is nonsymmetric (Scheme 7.2d). This means the polymer synthesis is more controlled and it is possible to achieve regiore-gular PPV materials. However, the monomers are more difficult to prepare (Scheme 7.3). Starting from the bis-sulfonium monomer 20, reaction with one... 

The first decision in choosing a synthetic method for a PPV material is the way in which the material will be processed (Scheme 7.8). The precursor routes will enable the preparation of solvent-resistant and more durable thin films of PPV. This is particularly desirable if a multilayer device structure is required for the application. When choosing different precursor methods, it is important to assess the criteria of the application. Most precursor methods involve a thermal elimination step to convert the precursor polymer to the PPV material. Sul-fonium precursors require higher-temperature elimination compared to sulfinyl precursors. This makes the sulfinyl route compatible with deposition on plastic substrates. Another factor to consider in precursor methods is the nature of the elimination byproducts. Sulfonium precursors convert to PPV with elimination of acids, such as HCl or HBr, which has been shown to be detrimental to device performance. Xanthate and dithiocarbamate routes involve the elimination of amine and CO2 and CS2, respectively. 

Sulfinyl or Louwet-VaruJerainde Precursor Route. The development of sulfinyl precursor polymers by Louwet et al. [996-998] has overcome many of the drawbacks of the previous precursor routes. 

Also, sulfinyl chlorides (precursors to sulfinate esters) have recently been prepared directly from disulfides (equation 3)23. 

Enantiomers (M)- and (P)-helicenebisquinones [32] 93 have been synthesized by high pressure Diels-Alder reaction of homochiral (+)-(2-p-tolylsulfo-nyl)-l,4-benzoquinone (94) in excess with dienes 95 and 96 prepared from the common precursor 97 (Scheme 5.9). The approach is based on the tandem [4 + 2] cycloaddition/pyrolitic sulfoxide elimination as a general one-pot strategy to enantiomerically enriched polycyclic dihydroquinones. Whereas the formation of (M)-helicene is explained by the endo approach of the arylethene toward the less encumbered face of the quinone, the formation of its enantiomeric (P)-form can be the result of an unfavourable interaction between the OMe group of approaching arylethene and the sulfinyl oxygen of 94. 

In addition to the HWE reactions leading to asymmetric vinyHc sulfoxides (not reviewed here), new recent appHcations of enantiopuxe a-sulfinylphospho-nates, such as their use as precursors of optically active di-alkyl or arylalkyl sulfoxides and also of 1 -sulfinyl-phosphonocyclopropanes, increases again their synthetic potential. 

Moreover, stereoselective titanium enolate additions to different iV-sulfinyl imines113 114 or in situ-prepared iV-arylimines (three-component reaction) have been carried out to afford the corresponding sulfinyl amides or valuable /3-amino acid precursors.115... 

S)-(+) -2-(p-TOLU NESULFINYL)-2-CYCLOPENTENONE PRECURSOR FOR ENANTIOSELECTIVE synthesis OF 3-SUBSTITUTED cyclopentanones (2-Cyclopenten-l-one, 2-[(4-methylphenyl)sulfinyl>, (S)-)... 

A new catalytic cycle for the enantioselective protonation of cyclic ketone enolates with sulfinyl alcohols has been developed (Scheme 2)25 In this method, the achiral alcohol plays two roles it is involved in the turnover of the chiral proton source and also in the generation of a transient enolate through the reaction of its corresponding alkoxide with the enol trifluoroacetate precursor. Stereoselectivity was found highly dependent on the structure of the achiral alcohol. 

The use of dimethyl (R)s-2-(10-isobornylsulfinyl)maleate (87) as a chiral synthetic equivalent of dimethyl acetylenedicarboxylate had several limitations arising from (i) the non-trivial preparation of the chiral auxiliary (10-mer-captoisoborneol) required to produce the dienophile, (ii) the low stereoselectivity observed in the synthesis of the thioether used as precursor of the sulfinyl reagent, and (iii) the lack of differentiation of the two ester groups present in the molecule. In order to avoid symmetrization, selective monodemethylation and further re-esterification were required as previous steps of desulfinylation (see... 

Sulfinyl sultam 82 was also used in the synthesis of enantiopure sulfinimines 85, useful precursors in the synthesis of enantiomerically pure amine, as well as a- and P-aminoacid derivatives.109 Interestingly, the addition of one equivalent of water to the sulfinylated HMDS 84 prior to the addition of the aldehyde was necessary to convert enolizable aldehyde into enantiomerically pure sulfinimines 85, which cannot be obtained by the Davis procedure. Thus, both enolizable and noneno-lizable aldehydes can afford enantiomerically pure aryl and alkyl sulfinimine 85 in good yield (Scheme 26). 

Sulfone stabilized carbanions attached at C-2 substantially accelerate the Claisen rearrangement (Scheme 22) these species may be generated from either regioisomeric precursors [142]. These processes take place with high levels of internal asymmetric induction [ 143], and the scope of the process is broad and it has been extensively studied. This acceleration was also noted for the related sulfinyl carbanions, albeit with low yields and in the case of sulfilimines no internal asymmetric induction was observed [144]. 

Diaryl Sulfoxides. Optically active diaryl sulfoxides are prepared by reaction of an aryl Grignard with (—)-menthyl (S)-p-toluenesulfinate 2,5-dimethoxyphenyl p-toly 1 sulfoxide (4), a precursor of sulfinyl quinones, and 3-pyridyl p-tolyl sulfoxide (5),... 

Similarly, in a total synthesis of strychnine, the optical resolution was carried out by separation of the sulfinyl lactam diastere-omers (7) and (8), which were obtained from the heptacyclic indole alkaloid precursor (6) this was first transformed with (/ )-(+)-p-tolylsulfinylacetic acid into the corresponding sulfinyl amide and then converted to the diastereomeric lactams (7) and (8) by an intramolecular conjugate addition (eq 3). ... 

Dimethyl sulfoxide (DMSO) can be used for carbon-carbon bond formation and as a precursor for the synthesis of stabilised sulfur ylides (see Chapter 3, p. 33). The sulfoxy S=0 group, like the sulfone (S02) group, has a stabilising effect on an adjacent carbanion hence, sulfinyl carbanions, like sulfonyl carbanions (see Chapter 10, p. 200), are useful reagents in organic synthesis. The carbanions (39) derived from alkylthioalkyl sulfoxides (38) are particularly valuable intermediates in syntheses (Scheme 21). 

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