Selenium heterocycles, reviews

In the book Organic Selenium Compounds Their Chemistry and Biology, edited by Klayman and Gunther, several chapters have been devoted to the review of selenium heterocycles including one chapter on... 

The scope of this chapter was first defined at the beginning of Chapter 3.16 in the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I). Since then, a general review on selenium heterocycles has been published . A few more specific works have also appeared... 

This review chapter focuses on the syntheses and reactions of these 5-membered heterocyclic ring systems containing nitrogen and sulfur (or selenium) (reported during 2006). The importance of these 71-rich heterocycles in medicinal chemistry and natural products is also covered. 

The extent of current interest in meso-ionic chemistry is illustrated by the fact that since the completion of the manuscript of this review a number of significant papers have been published. These include descriptions of four new representatives of the type A meso-ionic heterocycles. Three of these systems belong to the 144 structural possibilities described in Section IV. This brings the number of known type A meso-ionic systems up to forty-seven. The fourth new system is the first example of a type A meso-ionic heterocycle having a selenium atom in the meso-ionic ring. The extension of the general formula 19 to include selenium provides the possibility of a further 176 type A meso-ionic systems of which one is now known. The structures of these four new meso-ionic systems are given in Table A-I (appendix to Table I). 

Several recent reviews have included specific types of electrophilic cyclofunctionalization reactions.1 Important areas covered in these reviews are halolactonization u cyclofunctionalization of unsaturated hydroxy compounds to form tetrahydrofurans and tetrahydropyrans lb cyclofunctionalization of unsaturated amino compounds lc cyclofunctionalization of unsaturated sulfur and phosphorus compounds ld lf electrophilic heterocyclization of unconjugated dienes 1 synthesis of y-butyrolactones 1 h synthesis of functionalized dihydro- and tetrahydro-furans lj cyclofunctionalization using selenium reagents lk lm stereocontrol in synthesis of acyclic systems 1" stereoselectivity in cyclofunctionalizations lP and cyclofunctionalizations in the synthesis of a-methylenelactones.lq Previous reference works have also addressed this topic.2... 

The chemistry of six-membered heterocycles containing one selenium or tellurium atom was initially covered in CHEC-11(1996) (chapter 5.11). This updated chapter primarily deals with material dating from 1993 and is complete to 2005 with occasional references from 2006. The structures and nomenclature of the selenium- and tellurium-containing heterocycles discussed in this chapter are included in Figure 1. One major review of tellurium-containing heterocycles has appeared . The chemistry of thiopyrans, selenopyrans, and telluropyrans has also been reviewed <1994AHC180>. 

Alternative methods for the preparation of selenals and selones which could be applied to the synthesis of related selenium and tellurium heterocyclic systems have been recently reviewed <2005COFGT-II(3)397>. 

This review shows that the properties and comparative reactivity of five-membered heterocycles containing oxygen, sulfur, and selenium may place selenophene differently with respect to furan and thiophene, and its position in the series depends on the reaction and the role played by the heteroatom. Selenophene is located between furan and thiophene as regards reactions in which the heterocycle displays predominantly electron-donating properties as for those principally concerned with electron-accepting properties, selenophene is placed between thiophene and benzene. 

Similar, but less stable, selenium homocycles, as well as mixed sulfur-selenium related heterocycles formed by heteroatom replacement, are also well docnmented. Cationic chalcogen homocycles are also known and have been reviewed. ... 

There are a number of synthetically important applications, involving these heterocycles, as unstable intermediates, which are reviewed here. These applications feature the ability of selenium to be readily extruded from seleniranes and selenirenes, neighboring group participation by / -Se to control the stereochemistry of nucleophilic substitution reactions, and facile, chemoselective replacement of Se by H in radical-induced reactions. 

Heterocyclic Citemistry is an annual publication which combines material previously reviewed lo thiee separate SPR volumes - Saturated Heterocyclic Chemistry, Aromatic and Heteroaromatic Chemistry and the heterocyclic sections of Organic Compounds of Sulphur, Selenium, and Tellurium. ... 

Three earlier reviews cover thietanes and other derivatives up to the mid 1950s or 1960s Organic Compounds of Sulphur, Selenium and Tellurium, a Specialist Periodical Report of The Royal Society of Chemistry, includes reviews of smallring compounds (April 1969-March 1980 in six volumes). One chapter in Comprehensive Heterocyclic Chemistry gives a survey of four-membered sulfur hetero-cycles. A useful review on (2 + 2) cycloreversions covers some chemistry of relevance. ... 

Yamazaki [51] has reviewed a number of stoichiometric cycloaddition reactions at the cobaltacyclopentadiene ring system that lead to a plethora of heterocycles. For example, five- and six-membered heterocycles containing nitrogen, sulfur, selenium, and phosphorus have been made accessible by this route (eq. (20)) [52]. The co-cyclization of substituted alkynes and isocyanates in the presence of a rhodium metallocycle gives 2-pyridones (eq. (21)) [53]. 

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