Download Organoselenium Chemistry I: Functional Group Transformations by Professor Dr. Alain Krief, Professor Dr. László Hevesi PDF

By Professor Dr. Alain Krief, Professor Dr. László Hevesi (auth.)

During the final fifteen years organoselenium chemistry underwent a excellent mutation: from an unique zone of technological know-how practised by way of a number of experts it turned a comparatively good mastered and general technique of man-made natural chemistry. the main to this good fortune is reasonable variety of selenium dependent reagents and reactions were stumbled on, that are capable of practice particular adjustments selectively and sometimes less than very light stipulations. the purpose of this quantity is to give the various selenium containing reagents now to be had to chemists, to say the scope in addition to the restrictions in their reactions, and to match these which own related reactivities. The authors current the reagents within the order of accelerating oxidation point round the selenium atom.

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Extra info for Organoselenium Chemistry I: Functional Group Transformations

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In fact, a closely related reaction occurs with potassium thiocyanate, which instead leads to a stable episulfide [142]. Reaction of bromine in DMSO on olefins followed by reaction of the resulting bromohydrins with KSeCN allows the stereoselective (66-98 ss) (Z~E) or (e~Z) isomerisation of disubituted olefins [142] (Scheme 29). 2 Reduction of Epoxides and Thiiranes to OIefins Episelenides have also been postulated as intermediates in the deoxygenation of epoxides to olefins which occurs on reaction with potassium selenocyanate [144, 145, 160, 163] (Scheme 30), with triphenylphosphine selenide / trifluoroacetic acid [138] or with related compounds such as 1-phenyl-3,4-dimethylphospholeselenide or phospholene-3-selenide [164], with sodium diethyl phosphite / selenium [165,166], with 3-methyl-2-selenoxobenzothiazole [@167, 168] or with selenocarboxamides [@169] (readily available [170] from nitriles, carbon monoxide and selenium) the reactions being again performed in the presence of trifluoroacetic acid (Scheme 31).

Phenylseleno)trimethylsilane [148] (Scheme 40) and bis(trimethylsilyl) selenide [174] (Scheme 41) have a closely related reactivity. They reduce sulfoxides to sulfides [@148] as well as selenoxides [148] and telluroxides [148] to selenides and tellurides respectively (Schemes 40, 41). The reaction requires two equivalents of PhSeSiMe3, most probably involves onium intermediates [148] and occurs in the presence of a variety of other functional groups such as ketones, phenols, alcohols, sulfones, nitro groups and olefins which remain untouched during the process (Scheme 40).

Se° 300"C ~ • MeAJU 60% ro~ c) Me 2eq. Se° • 300-360°C/22h [200] no reaction [206] Me Me 2eq. Se° d) RO • 3OO0 Q7h Me Me Me ±590 Q? 0] octa-2,5-diene leads (in very low yield) to ethyl benzene and o-xylene when it is heated for 168h with selenium 49 3. 7eq. , Se° * • 350°Cl3Oh 40% Rl Rl Se° 350°C Rl R2 b) Me H 40h 40% c) H Me 32h 44% cxPw, CO - Se°* '- 450°C ~ Me d) e) CCE! 8% Scheme 67 [225] (Scheme 67) (see also Scheme 66d) [205]. Selenium powder in triphenylmethane has also been used [226] for the dehydrogenation of 2-aryl-2imidazolines to 2-aryl imidazoles (Scheme 68).

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