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1,3-dipolar cycloaddition of diaryldiazomethanes Ar 2 C N 2 across Cl 3 C–CH N–CO 2 Et 1 yields Δ 3 -1,2,4-triazolines 2 . Thermolysis of 2 leads, via transient azomethine ylides 3 , to diaryldichloroazabutadienes [Ar(Ar')C N–CH CCl 2 ] 4 . Treatment of 4a (Ar = Ar' = C 6 H 5 ) and 4c (Ar = Ar' = p -ClC 6 H 4 ) with NaSR in DMF yields 2-azabutadienes [Ar 2 C N–C(H) C(SR) 2 ] 5 . In contrast, nucleophilic attack of NaS t Bu on 4 affords azadienic dithioethers [Ar 2 C N–C(S t Bu) C(H)(S t Bu)] ( 7a Ar = C 6 H 5 ; 7b Ar' = p -ClC 6 H 4 ). The reaction of 4a with NaSEt conducted in neat EtSH produces [Ph 2 C N–C(H)(SEt)–CCl 2 H] 8 , which after dehydrochloration by NaOMe and subsequent addition of NaSEt is converted to [Ph 2 C N–C(SEt) C(H)(SEt)] 7c . Upon the reaction of 4c with NaS i Pr, the intermediate dithioether [( p -ClC 6 H 4 ) 2 C N–CH C(S i Pr) 2 ] 5k is converted to tetrakisthioether [( p - i PrSC 6 H 4 ) 2 C N–CH C(S i Pr) 2 ] 6 . Treatment of 4a with the sodium salt of piperidine leads to [Ph 2 C N–CH C(NC 5 H 10 ) 2 ] 10 . The coordination of 6 on CuBr affords the macrocyclic dinuclear Cu(I) complex 11 . The crystal structures of 5i , 7a , b , 10 and 11 have been determined by X-ray diffraction. [ABSTRACT FROM AUTHOR]

A wide range of electron-poor 4-bromo-/4-chloro-2-azabuta-1,3-dienes were synthesized by the Rh 2 (OAc) 4 -catalyzed reaction of diazo esters and diazo ketones with methyl 2-halo-2 H -azirine-2-carboxylates. The E stereoselectivity with respect to the configuration of the C C bond of the 2-azadiene moiety is in good agreement with the results of DFT (M06-2X/6-31+G(d,p)) calculations of the reaction pathway. The reaction proceeds via the formation of an azirinium ylide intermediate followed by ring opening with outward rotation of the halogen atom. Depending on the substitution pattern at C 1 electron-poor 4-halo-2-azabutadienes can undergo two types of cyclization at elevated temperatures: reversible 1,4-electrocyclization to give 2,3-dihydroazetes or 1,5- exo - trig cyclization to give 5-methylene-2,5-dihydrooxazoles, both in good yields. The dihydrooxazole derivatives can be also obtained at ambient temperature under DBU catalysis. [ABSTRACT FROM AUTHOR]

2-Amino-2-arylethylamides 1 carrying electron-donating substituents in the para position are transformed by hot POC1 to the the title compounds 2, presumably via iminochlorides 7 and imidazolium derivatives 8. Amides lacking this para-substituent give rise to chloroamidines 11 under these conditions. m-Methoxyphenethylamide 1t and POCl form, besides 11f, an isoquinoline derivative 3. The involvement of an imidazolium compound 8 in the formation of ethenamidines has been verified by the synthesis of 2a from 10. Reaction of amide 1w with PCl in the cold leads to, besides the chloroamidine 11c, the cis-ethenamidine 12 which equilibrates with the trans-isomer 2o in hot toluene. Thienylethyl urea 13 converted by hot POCl to the imidazoline 16, while phenylpropylamide 17 forms only the iminochloride 18a. [ABSTRACT FROM AUTHOR]