Synthesis of spiro-fused heterocyclic scaffolds through multicomponent reactions involving nitro ketene aminal (HKA)

Spiro heterocycles represent an important class of naturally occurring substances with biological properties. Spiro compounds having cyclic structures fused at a central carbon are of recent interest due to their interesting conformational features and their structural implications on biological systems. Spiro heterocycles have been found to play fundamental roles in biological processes. They have exhibited diversified pharmacological activities [1]. As a type of versatile building block for the synthesis of fused heterocycles, heterocyclic ketene aminals (HKAs) received much attention within the chemical community [2]. To continue our studies on the synthesis of pharmacologically active heterocyclic compounds using HKAs and considering the importance of spiro-fused frameworks in organic synthesis [3], herein we report an efficient synthesis of spirofused heterocyclic compounds 5 trough multi-component reactions of nitro ketene aminals derived from the addition of various diamines 1 to nitro ketene dithioacetal 2with o-phthalaldehyde 3 and 2-hydroxy-1,4-naphthoquinone 4 (Fig 1). This reaction proceeded without any catalyst in excellent yield and the other advantages of this work are simple work-up, no toxic byproducts and milder reaction conditions. All structures were confirmed by IR, 1H- and 13C-NMR analyses.