Epoxidation of 2-azabicyclo[2.2.1]hept-5-en-3-one

Epoxidation of 2-azabicyclo[2.2.1]hept-5-en-3-one has been performed in high yield with potassium hydrogen persulfate at pH 6, ¹H nmr data indicate an exo stereoconfiguration of the epoxide.     

Synthesis and Characterization of S-Methylspiro[4.5]-dec-7-en-6-one and 6-methylspiro[4.5]dec-6-en-8-one

In connection with another problem, we required authentic samples of 8-methylsiro[4.5]dec-7-en-6-one (1) and 6-methyl-spire[4.5]dec-6-en-8-one (2). The former compound is not reported in the literature. Although there are two reports of the latter material,^1,2 the physical data ascribed to it do not agree. In this communication, we report the synthesis and characterization of the two isomers.     

Synthesis of azolo[a]pyridines from 5-(bromomethyl)hept-4-en-3-one and 5-bromopent-3-en-2-one derivatives

Alkyl derivatives of 1H-imidazo[1,2-a]pyridin-4-ium, 5H-pyrido[1,2-a]benzimidazol-10-ium, 1H-[1,2,4]-triazolo[4,3-a]pyridin-4-ium, and 3-methylthiazolo[3,2-a]pyridin-4-ium bromides were obtained in two stages from (4Z)-5-(bromomethyl)-2,2,6,6-tetramethylhept-4-en-3-one, 5-bromo-4-methylpent-3-en-2-one, or (3E)-5-bromopent-3-en-2-one by alkylation of 1-alkyl-1H-imidazoles, 1-alkyl-1H-benz-imidazoles, 1-methyl-1H-1,2,4-triazole, and 4-methylthiazole and subsequent cyclization of the quaternary azolium salts in the presence of bases.     

Ring-opening polymerization of 2-azabicyclo-[2,2,1]-hept-5-en-3-one using metathesis catalysts

The ring-opening polymerization of an unsaturated bicyclic lactam, 2-azabicyclo-[2,2,1]-hept-5-en-3-one (ABHEO), was carried out using metathesis catalysts under various reaction conditions. It is observed that the best results (34% conversion and η_inh: 0.18 dL/g) were obtained when the mole ratios of ABHEO to WCl₆ as a catalyst and WCl₆ to AlEt₃ as a cocatalyst were 200 and 4, respectively. The infrared (IR) and nuclear magnetic resonance (¹H- and ¹³C-NMR) spectra of the polymer obtained indicated that the ABHEO was transformed to the ring-opened polymer, poly(2-pyrrolidone-3,5-diylvinylene) [poly(ABHEO)]. The resulting polymer was amorphous as determined by DSC analysis, which showed only secondary transition at 100°C.     

The Carbonyl Group as Homoconjugated Electron-Releasing Substituent. Regioselective electrophilic additions at bicyclo[2.2.1]hept-5-en-2-one,bicyclo[2.2.2]oct-5-en-2-one,and derivatives

In CHCl₃, CH₃CN, or AcOH, benzeneselenenyl chloride (PhSeCl), bromide (PhSeBr), and acetate (PhSeOAc), 2-nitrobenzenesulfenyl chloride (NO₂C₆H₄SCl), and 2,4-dinitrobenzenesulfenyl chloride ((NO₂)₂C₆H₃SCl) added to bicyclo[2.2.1]hept-5-en-2-one ( 5 ) in an. anti fashion with complete stereo- and regioselectivity, giving adducts 20–24 in which the chloride, bromide, or acetoxy substituent (X) occupies the endo position at C(6) and the Se- or S-substituent (E) the exo position at C(5), The addition 5 + (NO₂)₂C₆H₃SCl→ 24 was accompanied by the formation of (1RS, 2RS)-2-(2,4-dinitrophenylthio)cyclopent-3-ene-l-acetic acid ( 25 ). The latter was the major product in AcOH containing LiClO₄. The additions of PhSeCl and PhSeBr to bicyclo[2.2.2]oct-5-en-2-one ( 6 ) were less stereoselective (proportion of exo vs. endo mode of electrophilic attack was ca. 3:1) but highly regioselective gazing adducts 27/28 and 29/30 , respectively, the regioselectivity being the same as that of the electrophilic additions of 5 . The reaction of PhSeCl with a 4:1 mixture of 2-exo-chloro- and 2-endo-chlorobicyclo[2.2.1]hept-5-ene-2-carbonitriles ( 12 ) was slower than addition 5 + PhSeCl; it gave adducts 31/32 (4:1) in which the PhSe moiety occupies the exo position at C(6) and the Cl atom the endo position at C(5). The addition of PhSeCl to 2-chlorobicyclo[2.2.1]oct-5-ene-2-carbonitriles ( 13 ) was very slow and gave adducts with the same regioselectivity as 12 + PhSeCl, but opposite with that of reactions of the corresponding enones 5 and 6 . PhSeX (X = Cl, Br, OAc) added to 2-cyanobicyclo[2.2.1]hept-5-en-2-yl acetates ( 14 ) with the same regioselectivity as 12 + PhSeCl. The additions of PhSeCl, PhSeBr, NO₂C₆H₄SCl, and (NO₂)₂C₆H₃SCl to 2-(bicyclo[2.2.1]hept-5-en-2-ylidene)propanedinitrile ( 49 ) were not regioselective, showing that a dicyanomethylidene function is not like a carbonyl function when homoconjugated with a π system. The results are in agreement with predictions based on MO calculations suggesting that a carbonyl group homoconjugated with an electron-deficient centre can behave as an electron-donating, remote substituent because of favourable n(CO)?σC(1), C(2)?p(C(6) hyperconjugative interaction.     

Novel dimerisation of bicyclo[3.3.0]oct-2-en-3-one

Application of the intramolecular Wadsworth-Emmons reaction to bicyclo[3..3.0]oct-2-en-3-ones results in the formation of a novel dimer (11) of the parent member (6) whose structure has been determined by X-ray crystallography.     

Hydroarylation of 2-azabicyclohept-5-en-3-one

The hydroarylation of 2-azabicyclo[2.2.1]hept-5-en-3-one with a range of aryl iodides is presented.