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Novel tricyclic pyrimidine-fused 8-membered heterocycles were prepared by an iminium ion cyclization using pyrimidinediamine systems with electron-rich aromatic rings.

The mechanism of the cycloaddition reaction between singlet state unsaturated silylene dichlorosilylenesilylene [Cl2Si = Si:] and ethylene, which generates a silicic bis-heterocyclic compound, has been investigated with the CCSD(T)//MP2/6-31G* method. The calculations show that the dominant reaction pathway consists of three steps. (I) The 3p unoccupied orbital of the Si atom in dichlorosilylenesilylene [Cl2Si = Si:] (R1) and the π-orbital of ethylene (R2) firstly form a π → p donor-acceptor bond, which makes the two reactants generate a three-membered cyclic intermediates (INT) through a barrier-free exothermic reaction of 127.7 kJ mol-1. (II) INT then isomerises to a four-membered cyclic silylene (P1) by the ring-expansion effect, which is via a transition state (TS1) with an energy barrier of 6.4 kJ mol-1. (III) sp3 hybridisation of the Si atom finally makes P1 react directly with ethylene to form a silicic bis-heterocyclic compound (P2) without any intermediates and transition states, and this step is also a barrier-free exothermic reaction of 138.6 kJ mol-1. [ABSTRACT FROM AUTHOR]

The mechanism of the sulfur extraction reaction between singlet germylene carbene and its derivatives [X2GeC: (X = H, F, Cl, CH3)] and thiirane has been investigated with density functional theory, including geometry optimization and vibrational analyses for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by B3LYP/6‐311G(d,p) method. From the potential energy profile, it can be predicted that the reaction pathway of this kind consists two steps: (1) the two reactants firstly form an intermediate (INT) through a barrier‐free exothermic reaction; (2) the INT then isomerizes to a product via a transition state (TS). This kind reaction has similar mechanism, when the germylene carbene and its derivatives [X2GeC: (X = H, F, Cl, CH3)] and thiirane get close to each other, the shift of 3p lone electron pair of S in thiirane to the 2p unoccupied orbital of C in X2Ge = C: gives a p → p donor–acceptor bond, leading to the formation of INT. As the p → p donor–acceptor bond continues to strengthen (that is the CS bond continues to shorten), the INT generates product (P + C2H4) via TS. It is the substituent electronegativity that mainly affects the extraction reactions. When the substituent electronegativity is greater, the energy barrier is lower, and the reaction rate is greater. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The mechanism of the cycloaddition reaction between singlet dichloro-germylene carbene and aldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by zero-point energy and CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (A) consists of four steps: (1) the two reactants (R1, R2) first form an intermediate INT2 through a barrier-free exothermic reaction of 142.4 kJ/mol; (2) INT2 then isomerizes to a four-membered ring compound P2 via a transition state TS2 with energy barrier of 8.4 kJ/mol; (3) P2 further reacts with aldehyde (R2) to form an intermediate INT3, which is also a barrier-free exothermic reaction of 9.2 kJ/mol; (4) INT3 isomerizes to a germanic bis-heterocyclic product P3 via a transition state TS3 with energy barrier of 4.5 kJ/mol. The process of channel (B) is as follows: (1) the two reactants (R1, R2) first form an intermediate INT4 through a barrier-free exothermic reaction of 251.5 kJ/mol; (2) INT4 further reacts with aldehyde (R2) to form an intermediate INT5, which is also a barrier-free exothermic reaction of 173.5 kJ/mol; (3) INT5 then isomerizes to a germanic bis-heterocyclic product P5 via a transition state TS5 with an energy barrier of 69.4 kJ/mol. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of the cycloaddition reaction of forming germanic bis-heterocyclic compound between singlet germylene carbene and acetone has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction of forming germanic bis-heterocyclic compound consists of three steps: (1) the two reactants firstly form an intermediate INT4 through a barrier-free exothermic reaction of 181.4kJ/mol; (2) INT4 further reacts with acetone (R2) to form an intermediate (INT5), which is also a barrier-free exothermic reaction of 148.9kJ/mol; (3) INT5 then isomerizes to a germanic bis-heterocyclic product P5 via a transition state TS5 with an energy barrier of 53.3kJ/mol. [Copyright &y& Elsevier]

7,8,9-Trisubstituted dihydropurine derivatives were prepared from 5-amino-4-(N,N-disubstituted)aminopyrimidines and aromatic aldehydes via a cascade of reactions. The key transformation for the reaction is a [1,6]-hydrogen shift due to a ‘tert-amino effect’. [ABSTRACT FROM AUTHOR]