A novel and facile carbodiimide-mediated synthesis of 2,3-dihydro-6H-pyrimido[2,1-b]quinazolin-4(1H)-ones via a tandem intramolecular nucleophilic addition/intramolecular hetero conjugate addition annulation strategy

Synthesis of Diazaheterocyclic Ring‐Fused 1,2,4‐Benzothiadiazine 1,1‐Dioxides by a Sequential Aza‐Wittig/NH‐Addition Cyclization/Nucleophilic Ring‐Closure Methodology with N‐Alkenyl‐2‐carbodiimidobenzenesulfonamides as Key Intermediates

“…[1] One of the most convenient synthetic methods for cyclic guanidines would be nucleophilic addition of a nitrogen species to a functionalized carbodiimide. Many groups (Molina, [2] Wamhoff, [3] Ding, [4] Quintela, [5] Eguchi, [6] Noguchi, [7] Nitta, [8] and Abe [9] ), also including our own, [10] have independently developed various (tandem) processes involving aza-Wittig reactions between iminophosphoranes and isocyanates to give functionalized carbodiimides, followed by various types of ring-forming reaction (Scheme 1). [11] These variously functionalized carbodiimides undergo initial cyclizations onto the cumulene functionality, in the forms of: a) intramolecular addition of a nitrogen nucleophile, [6b,9c,10b] b) electrocyclization, [5a] c) intermolecular [4 + 2] cycloaddition, [8a,8b] or d) intermolecular nucleophilic addition of an amine and various subsequent types of ringforming reactions between the acyclic guanidine nitrogen and the available inner functional group, to give monocyclic guanidines A.…”

A Facile Synthesis of 4(3H)-Pteridinone Derivatives by Utilizing N-{3-[(N-Substituted)carbamoyl]-2-pyrazyl}iminophosphoranes

“…As well as other workers we have also recently demonstrated that the intramolecular aza-Wittig reaction is a powerful and useful tool for the synthesis of 5-8 membered heterocycles 2, 5,6 including natural products such as DC-81, 7,8 l -vasicinone, 9 (-)-benzomalvin A, 10 (-)-dendrobine, 11 and (+)-fumiquinazoline G 12 etc. On the other hand, the intermolecular aza-Wittig reaction followed by electrocyclization, cycloaddition or heterocyclization, i.e., the tandem aza-Wittig methodology, has been utilized for the synthesis of many important heterocycles by Molina, 3 Wamhoff, 4 Quintela, 13 Saito, 14,15 and Noguchi 16,17 and co-workers. We were interested in the preparation and the reactivity of the N -heteroaryliminophosphorane derivatives because these species seem to have been less studied, notwithstanding their promising role as building blocks for synthesis of heterocyclic compounds.…”