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Nukleofilowe podstawienie wodoru w nitroarenach. Proces analogiczny i komplementarny do podstawienia elektrofilowego

Mąkosza M.

Wiadomości Chemiczne

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2011

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[Z] 65, 9-10

795-819

EN

Nucleophiles add to electron-deficient arenes, also those containing halogens, initially in positions occupied by hydrogen to form óH adducts. This addition is faster than addition in similarly activated positions occupied by halogens. Formation of the óH adducts is a reversible process, thus they dissociate and slower addition in positions occupied by halogens results in formation of óH adducts followed by fast departure of X– to form products of nucleophilic substitution of halogen, SNAr. In the review it is shown that there are a few ways for fast further conversion of initially formed óH adducts into products of nucleopilic substitution of hydrogen such as oxidative substitution, vicarious substitution, etc. Since formation of óH adducts is faster than óH adducts and the former undergo fast transformations into products of nucleophilic substitution of hydrogen we should accept than this is the major, primary reaction whereas conventional nucleophilic substitution of halogens, SNAr reaction “ipso” substitution is just a secondary process. In modern textbooks only SNAr reactions are discussed whereas nucleophilic substitution of hydrogen is not mentioned, thus it is necessary to introduce proper corrections in textbooks and teaching of this chapter of chemistry of arenes.

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Synteza koroli

Koszarna B., Gryko D.T.

Wiadomości Chemiczne

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2008

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[Z] 62, 3-4

165-185

EN

Corroles, one carbon shorter analogues of porphyrins emerged a few years ago as an independent research area (Fig. 1) [1-3]. Their coordination chemistry, photophysics, synthesis, chemical transformations, electrochemistry and other properties have recently been studied in great detail [7-11]. Discovered in 1964 [15], for many years they have been mainly synthesized via a,c-biladienes cyclization [19-20]. Multistep a,c-biladienes preparation discouraged broader range of chemists from studying corroles (Scheme 2). Since initial reports by Gross [17, 18] and Paolesse [16] revealing one-pot syntheses of meso-substituted corroles from aldehydes and pyrrole, this reaction has been subjected to many refining studies (Scheme 4, 5; Table 2) [23-28]. As a result yields have been improved to ~ 15%. The one-pot synthesis of meso-substitued A3-corroles from aldehydes and pyrroles consists of two independent steps. The first step is an acid-mediated electrophilic substitution to yield a mixture of various aldehyde-pyrrole oligocondensates including bilane (tetrapyrrane) - the direct precursor of corrole (Scheme 6). The second step is the oxidative ring-closure. Maximizing bilane formation while minimizing the formation of dipyrromethanes, tripyrrane and higher oligocondensate is a difficult task due to the similar reactivity of all these compounds [30-32]. Recently new and efficient conditions for the synthesis of meso-substituted corroles have been developed [33]. The first step, namely the reaction of aldehydes with pyrrole, was carried out in a water-methanol mixture in the presence of HCl. A relatively narrow distribution of aldehyde-pyrrole oligocondensates was controlled by their solubility in the reaction medium. After thorough optimization of various reaction parameters high yields of bilanes were obtained. As a result, many A3-corroles were obtained in the highest yield (~25-30%) reported to date. Corroles bearing two various substituents at meso positions were synthesized for the first time from dipyrromethanes and aldehydes (Scheme 10) [35]. This method continues to prevail in the literature [36-38]. Performance of this reaction in H2O/MeOH/HCl mixtures allows to obtain trans-A2B-corroles in yields up to 56% (Scheme 11) [33]. Last developments in the chemistry of corroles make these compounds more accessible than respective porphyrins.

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Syntetycznie użyteczne reakcje pochodnych cyklopropenonu

Zając A., Girek T.

Prace Naukowe. Chemia i Ochrona Środowiska / Akademia im. Jana Długosza w Częstochowie

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2008

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Vol. 12

53-82

PL

Omówiono metody syntezy i reaktywność cyklopropenonu i jego wybranych pochodnych, opisano również ich niektóre właściwości fizykochemiczne.

EN

Syntheses and reactivity of cyclopropenone and its selected derivatives are presented. Some properties of these compounds are also described.