Six-Membered Selenium-Nitrogen Heterocycles

Six-Membered Selenium Heterocycles WITH One Nitrogen Atom 

The first derivative of this ring system, 2-imino-2,3.5.6-tetrahydro-l,3-selenazine (216), was obtained through the reaction of l-bromo-3-amino-propane with potassium selenocyanate. [Eq. (51)]. 

More recently, perhydro-l,3-selenazines (219) were prepared by the reaction of bis-(3-phthalimidopropyl)diselenide (217) with hydrazine hydrochloride to give the diselenide 218. Reduction of the latter with sodium in liquid ammonia followed by treatment with aldehydes or ketones gave the selenazines 219 ° [Eq. (52)]. 

Selenourea and 1-aryl and 1,3-diaryIselenoureas reacted with acetylene-dicarboxylic acid and its dimethyl ester to give 3,4-dihydro-2-imino-2/f-l,3-selenazin-4-one-6-carboxylic acid derivatives, e.g., 220 and 221. The structure of 221 was deduced from that of its hydrogenation product 222.  

Reaction of the 1,3-selenazine derivative 223 with A(-methylquinaldinium salts is reported to give the quinolinidene derivative 224 (X = S) and its 0X0 derivative (X = O). Lepidinium derivatives behaved similarly.  

Six-Membered Selenium Heterocycles with One Nitrogen Atom 

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A. Six-Membered Selenium Heterocycles with One Nitrogen Atom.144... 

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]. 

There are a number of six-membered heterocycles which contain selenium or tellurium, and two other heteroatoms other than nitrogen, for example, the reaction of formaldehyde and hydrogen selenide gives 1,3,5-oxadiselenane (238) and 1,3,5-dioxaselenane (239 R = Me) <82ZAAC(488)60>. Similarly, acetaldehyde in aqueous acidic solution reacts with hydrogen selenide to afford 2,4,6-trimethyl-1,3,5-dioxaselenane (239 R = Me) <67JCS(B)il7>. 

This chapter is one of the first attempts of systematic review of the synthetic methods and chemistry of nonaromatic saturated and unsaturated perfluorinated heterocycles. It summarizes data on the synthesis and chemical transformation of perfluorinated six- and to some extent five- membered nonaromatic heterocyclic compounds containing oxygen, nitrogen, sulfur, selenium, and phosphorous. It should be pointed out that the review is not all-inclusive one, but it is an attempt to provide representative examples of synthetic methods and chemistry of perfluorinated nonaromatic hetero-cychc materials. 

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