Intramolecular 4 + 3 Cycloadditions. Theoretical and Experimental Evaluation of Endo/Exo Preferences of a Cyclopentenyl Cation (original) (raw)
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An MC-SCF study of the thermal cycloaddition of two ethylenes
Journal of The American Chemical Society, 1985
stable species on the potential energy surface of CH302+. dications is not questioned by the result. It should also be mentioned that in line with the theoretical results, neither spontaneous nor collision-induced dissociation of CH302+-dications to either CH2+./OH+ and HC+/H20+-(eq 3 and 4, Scheme I) has been observed.
J. Am.Chem.Soc. 1988, 110, 3247-3252.pdf
Acid-catalyzed rearrangement of 6-bromo-2,4-dimethyl-4-(phenylamino)cyclohexa-1 ,4-dienone (1, a quinamine) in aqueous methanol gives, from a so-called quinamine rearrangement, 4'-amino-6-bromo-2,4-dimethyldiphenyl ether (2) and a number of byproducts. The ratio of yield of 2 to that of byproducts is 76:24. The byproducts are, mostly, 1,3-dimethylcarbazole (7) and some of its derivatives, the relative yields of which depend on the concentration of the catalyzing acid, HCI. The major byproduct in low HC1 concentrations is 1,3-dimethyl-4-methoxycarbazole (9). Kinetic isotope effects (KIE) were measured for the formation of 2 from 1, which was labeled at the carbonyl oxygen atom (['*0]-1), the nitrogen atom ([I5N]-1), and the para position of the aniline ring ([4-I4C]-1). The KIE (averages) were as follows: k ( ' 6 0 ) / k ( 1 8 0 ) , 1.0399; k(I4N)/k(l5N), 1.0089; /~( ' * c ) / k (~~C ) , 1.0501. The results suggest that the formation of 2 is a concerted process, a [5,5]-sigmatropic rearrangement, and not a two-step one, going through the rate-determining formation of a r-complex. KIE were measured for the formation of both 2 and 9 from 1, which was labeled in the ortho position of the anilino ring ([2-14C]-1). The KIE [k(12C)/k(14C)] were respectively 0.9895 and 1.0697. These results suggest that the byproduct (9) is formed by a concerted process, too, a [3,3]-sigmatropic rearrangement to an intermediate , which continues on to 9 and the other byproducts. The results show also that 2 cannot be formed from 1 by a succession of two [3,3]-sigmatropic rearrangements, the first of which is to 14. Thus, the quinamine rearrangements. on the basis of our results with 1, appear to be concerted, rather than a-complex intermediate, processes.
Russ. Chem. Bull., Int. Ed. 2004, 53, №4, 860-872
The intramolecular Diels-Alder reaction of readily accessible 4 substituted 4 (N fur furyl)aminobut 1 enes was studied and a new one step method was developed for the synthesis of 6,8a epoxy 1,2,3,4,4a,5,6,8a octahydroisoquinoline (3 aza 11 oxatricyclo[6.2.1.0 1,6 ]undec 9 ene) derivatives. The [4+2] cycloaddition proceeds stereoselectively to form exo adducts. The influence of substituents at the nitrogen atom in 4 (N furfuryl)aminobut 1 enes on the cycloaddition pathway was examined. , 3 aza 11 oxatricyclo[6.2.1.0 1,6 ]un dec 9 enes. Table 5. Spin spin coupling constants (J ) of protons in the 1 H NMR spectra of solutions of homoallylamines 1a-j and 4a,b (CDCl 3 ) Com J/Hz pound J 1,1 J 1cis,2 J 1trans,2 J 2,3 J 3A,4 J NCH(A)H(B) J of furan H atoms Other J α,β α ,β´β,β1
J. Org.Chem. 1982, 47, 2055-2060.pdf
h. 1BF NMR analysis (standard C&,CFJ showed that cycloadduct 15 was formed in 63% yield (cis,truns-15/truns,truns-l5 ratio of 83/17). The reaction mixture was submitted to methanolysis in a manner similar to that for the desilylation of 14.
J. Org. Chem. 2009, 74, 2780–2787.pdf
The enantioselective hydrogenation of 2-benzylquinolines and 2-functionalized and 2,3-disubstituted quinolines was developed by using the [Ir(COD)Cl] 2 /bisphosphine/I 2 system with up to 96% ee. Moreover, mechanistic studies revealed the hydrogenation mechanism of quinoline involves a 1,4-hydride addition, isomerization, and 1,2-hydride addition, and the catalytic active species may be a Ir(III) complex with chloride and iodide. tion of quinoline derivatives using [Ir(COD)Cl] 2 /MeO-BiPhep/I 2 as catalyst with high enantioselectivity, 7 and this methodology has been successfully applied to the synthesis of some tetrahydroquinoline alkaloids. 8 † (1) For some reviews and books on hydrogenation of aromatic compounds, see: (a) Rylander, P. N. Barbaro, P.; Scapacci, G.; Farnetti, E.; Graziani, M. Organometallics 1998, 17, 3308-3310. (b) Henschke, J. P.; Burk, M. J.; Malan, C. G.; Herzberg, D.; Peterson, J. A.; Wildsmith, A. J.; Cobley, C. J.; Casy, G. Kashiwabara, M.; Sato, K.; Ito, T.; Kaneda, K.; Ito, Y. Tetrahedron: Asymmetry 2006, 17, 521-535. (5) Kuwano, R.; Kashiwabara, M.; Ohsumi, M.; Kusano, H. J. Am. Chem. Soc. 2007, 129, 808-809. (6) (a) Ohta, T.; Miyake, T.; Seido, N.; Kumobayashi, H.; Takaya, H.
Journal of The American Chemical Society, 1999
High level ab initio MO calculations have identi®ed two complexes of borane with 2-¯uoropropane. In the ®rst, the boron atom is above the small C1,C2,C3 angle (in complex); in the other, the boron atom is outside that angle (out complex). The ionization to form the 2-propyl cation and the trihydro¯uoroborate ion A was followed by lengthening the C±F bond, d, in each complex and reoptimizing all other geometrical parameters. It was concluded that ionization occurred at d 1:8±2:0 A: The out ionization pathway was of lower energy (1±2 kcal/mol at MP2(FC)/6-31G pp ) at al values of d. A third pathway (top), in which the F±B bond was held perpendicular to the C1,C2,C3 plane, rather than allowed to tilt, was 8±9 kcal/mol higher in energy throughout. Ionization to the tight ion pair did not require a large energy expenditure (19.0 kcal/mol over the isolated reactants at d 2:00 A; 30.3 kcal/mol at d 2:20 A). A medium of dielectric constant 8.93, in SCRF(IPCM)-MP2(FC)/6-31G pp yyMP2/6-31G pp calculations, reduced the ionization energy to 14.2 kcal/mol at d 2:20 A: The dielectric medium also reorders the relative energy of the three orientations to out , top (1.0 kcal/mol) ,in (4.5 kcal/mol), at d 2:20 A: Changes in bond lengths and angles show hyperconjugative assistance to the ionization by the methyl hydrogens anti to the¯uorine along all pathways. As the ions separate, this effect decreases and. the interaction with the anion of one of the hydrogens initially syn to the¯uorine becomes important. Along the in pathway, rotation of one of the methyl groups occurred along the in pathway at 2.20 A Ê and elimination at 2.30 A Ê ; along the top pathway, it occurred at 2.30 and 2.40 A Ê , respectively. Along the out pathway, methyl group rotation brought a hydrogen in each close to the anion at d 2:50 A and elimination followed at 2.70 A Ê . The top orientation had not eliminated at distances about 2.6 A Ê and higher in our previous work. Both the in and out forms were optimized without elimination at d 2:80 A with tetra¯uoroborate (C) as anion. The calculations predict features of solvolyses, such as transfer of a nucleophile from the backside of the anion (retentive solvolysis), elimination to ole®n within the ion pair, and recombination at the backside of the anion (oxygen scrambling faster than racemization of tosylates and carboxylates). q