Recent progress towards the transition-metal-catalyzed Nazarov cyclization of alkynes via metal carbenes

In recent years, transition-metal-catalyzed tandem cyclization reaction of alkyne, especially involving metal carbene intermediate, has received worthwhile interest as it bypasses the employment of risky and potentially explosive diazo compounds as beginning materials for carbene generation. The Nazarov cyclization based on 4π-conrotatory electrocyclization of a conjugated pentadienyl cation to afford a cyclopentenyl cation is a significant and general strategy for the stereospecific synthesis of 5-membered cycles. In this review, we introduce an overview of recent advances in the transition-metal-catalyzed Nazarov cyclization of alkynes via metal carbene intermediate, and categorize these reactions according to the structure of metal carbene so as to accelerate advancement in this enchanting area for study.