• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.2155-2157
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• 2009

• Bulletin of the Korean Chemical Society
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• v.24 no.8
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• pp.1141-1149
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• 2003

The structures and gas-phase ionization energies (ΔG°) of Meldrum's acid (I) and related cyclic (II-VI) and acyclic compounds (VII-IX) are investigated theoretically at the MP2/6-31+$G^*$, B3LYP/6-31+$G^*$, B3LYP/6- 311+$G^{**}$, B3LYP/6-311++G(3df,2p) and G3(+)(MP2) levels. Conformations of three neutral cyclic series vary gradually from boat (Meldrum's acid, I), to twisted chair (II) and to chair (III) as the methylene group is substituted for the ether oxygen successively. The preferred boat form of I can be ascribed to the two strong $n_O$ → σ* c-c antiperiplanar vicinal charge transfer interactions and electrostatic attraction between negatively charged C¹ and positively charged C⁴at the opposite end of the boat. All the deprotonated anionic forms have half-chair forms due to the two strong $n_C$ → π* c=0 vicinal charge transfer interactions. The dipole-dipole interaction theory cannot account for the higher acidity of Meldrum's acid (I) than dimedone (III). The origin of the anomalously high acidity of I is the strong increase in the vicinal charge transfer ($n_C$ → π* c=0) and 1,4-attrative electrostatic interactions (C¹↔C⁴) in the ionization (I → $I^-$ + $H^+$). In the acyclic series (VII-IX) the positively charged end atom, C⁴, is absent and the attractive electrostatic stabilization (C¹↔C⁴) is missing in the anionic form so that the acidities are much less than the corresponding cyclic series.

• Bulletin of the Korean Chemical Society
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• v.24 no.2
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• pp.193-196
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• 2003

Nucleophilic addition reactions of benzylamines $(XC_6H_4CH_2NH_2)$ to benzylidene Meldrum's acids (BMA; $YC_6H_4CH=C(COO)_2C(CH_3)_2$) have been investigated in acetonitrile at 20.0 ℃. The rates of addition are greatly enhanced due to the abnormally high acidity of Meldrum's acid. The magnitudes of the Hammett $({\rho}_X\;and\;{\rho}_Y)$ and Bronsted $({\rho}_X$)$ coefficients are rather small suggesting an early transition state. The sign and magnitude of the cross-interaction constant, ${\rho}_{XY}$ (= -0.33), and kinetic isotope effects $(k_H/k_D\;{\stackrel}{~}{=}\;1.5-1.7)$ involving deuterated benzylamine nucleophilies $(XC_6H_4CH_2ND_2)$ are indicative of hydrogen-bonded cyclic transition state. The activation parameters, ${\Delta}H^{\neq}\;{\stackrel}{~}{=}\;4\;kcal\;mol^{-1}\;and\;{\Delta}S^{\neq}\;{\stackrel}{~}{=}\;-37\;e.u.$, are also in line with the proposed mechanism.

• Bulletin of the Korean Chemical Society
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• v.27 no.4
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• pp.503-507
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• 2006

The rhodium(II)-catalyzed reactions of diazo compound derived from Meldrum's acid with a variety of styrenes have been examined. These reactions provide a rapid route to the preparation of cyclopropanes with a variety of substituents on the benzene ring. The mechanistic pathway for the formation of these products has been also described in terms of a stepwise mechanism.

• Bulletin of the Korean Chemical Society
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• v.28 no.7
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• pp.1203-1205
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• 2007