Zwitterion from a Cyclopropane with Geminal Donor and Acceptor Groups

Abstract

2,2-Dimethoxy-3,3-dicyanospiro[cyclopropane-1,9'-[9H]fluorene] reacted fast with methanol to afford 9-trimethoxymethyl-9-dicyanomethyl-9H-fluorene. Reaction with benzaldehydes also gave products of cyclopropane ring opening. Strong electron-donor p-substituents or a strong attractor enhanced the rate. Ring opening of the cyclopropane to a zwitterion that recloses or reacts with an aryl aldehyde, to form either a CO or a CC bond first, can explain the result. The former mode of closure is sensitive to p-substituents because they are directly conjugated to the positive charge at the benzylic carbon of the former aldehyde. The latter mode is sensitive to the ground-state electrophilicity of the carbonyl carbon of the former aldehyde. Thus, reaction of the cyclopropane with p-substituted aldehydes is accelerated by either electron-donor or -acceptor substituents. [reaction: see text].

The First Reaction of Dimethoxycarbene with an Imine Moiety

“…Despite the mechanistic consideration, the presented results show that DMC can in principal react with an electron-deficient imine group. In contrast to the analogous reaction with an electron-deficient ethylene derivative [23] …”

Synthesis of Saturated Heterocycles via Metal-Catalyzed Formal Cycloaddition Reactions That Generate a C–N or C–O Bond

“…[21][22] The existence of such "intimate ion pairs" has also been proposed by other authors. [23][24][25] A stereoselective anti attack of the aldehyde followed by a fast bond rotation of 120 °C would lead to the favored envelope conformation IV, in which all groups are in favorable pseudo-equatorial positions. Finally, C-C bond formation would give the observed tetrahydrofuran.…”

A Combined Experimental and Theoretical Study of the Polar [3 + 2] Cycloaddition of Electrophilically Activated Carbonyl Ylides with Aldehydes and Imines

“…7 The first one is the thermal opening of the epoxide 1a, 26.9 kcal/mol, proved to be slightly higher than that associated with the thermal opening of the cyclopropane ring on the 2,2-dimethoxy-3,3-dicyanospiro[cyclopropane- 1,9'-[9H]fluorene recently reported by Warkentin, 24.4 kcal/mol. 8 However, the formation of the corresponding carbonyl ylide CYa was lesser endothermic, 11.7 kcal/mol, that the corresponding zwitterion intermediate, 22.8 kcal/mol. Interestingly, the zwitterion proposed by Warkentin was captured by benzaldehyde to yield a formally [3+2] cycloadduct, which showed the same regioselectivity than that found on the reaction of CYa with isatin.…”

“…Crystal data for 5a (colorless prisms): C 21 H 20 N 2 O 6 , M r = 396.39, monoclinic, space group P 2 1 , a = 7.8658(7), b = 8.6374(8), c = 15.3824(16) Å,  = 99.533(5) °, V = 1030.65(17) Å3 , Z = 2,  calcd = 1.277 g.cm -3 ,  = 0.095 mm-1 . A final refinement on F 2 with 2497 unique intensities and 262 parameters converged at R(F 2 ) = 0.0812 (R(F) = 0.0359) for 2359 observed reflections with I > 2(I).Crystallographic data were deposited in CSD under CCDC registration number 688228.Crystal data for 6a (colorless prisms): C 18 H 12 N 2 O 4 , M r = 320.30, monoclinic, space group P 2 1 /a, a = 13.4303(7), b = 7.8903(4), c = 13.9246(6) Å,  = 91.425(3) °, V = 1475.12(12) Å 3 , Z = 4,  calcd = 1.442 g.cm -3 ,  = 0.104 mm-1 .…”