In Pursuit of Synthetic Efficiency: Convergent Approaches

Abstract

Conspectus The field of total synthesis has reached a stage in which emphasis has been increasingly focused on synthetic efficiency rather than merely achieving the synthesis of a target molecule. The pursuit of synthetic efficiency, typically represented by step count and overall yield, is a rich source of inspiration and motivation for synthetic chemists to invent innovative strategies and methods. Among them, convergent strategy has been well recognized as an effective approach to improve efficiency. This strategy generally involves coupling of fragments with similar complexity to furnish the target molecule via subsequent cyclization or late-stage functionalization. Thus, methodologies that enable effective connection of fragments are critical to devising a convergent plan. In our laboratory, convergent strategy has served as a long-standing principle for pursuing efficient synthesis during the course of planning and implementing synthetic projects. In this Account, we summarize our endeavors in the convergent synthesis of natural products over the last ten years. We show how we identify reasonable bond disconnections and employ enabling synthetic methodologies to maximize convergency, leading to the efficient syntheses of over two-dozen highly complex molecules from eight disparate families. In detail, we categorize our work into three parts based on the diverse reaction types for fragment assembly. First, we demonstrate the application of a powerful single-electron reducing agent, SmI2, in a late-stage cyclization step, forging the polycyclic skeletons of structurally fascinating Galbulimima alkaloids and Leucosceptrum sesterterpenoids. Next, we showcase how three different types of cycloaddition reactions can simultaneously construct two challenging C–C bonds in a single step, providing concise entries to three distinct families, namely, spiroquinazoline alkaloids, gracilamine, and kaurane diterpenoids. In the third part, we describe convergent assembly of ent-kaurane diterpenoids, gelsedine-type alkaloids, and several drug molecules via employing some bifunctional synthons. To access highly oxidized ent-kaurane diterpenoids, we introduce the hallmark bicyclo[3.2.1]­octane ring system at an early stage, and then execute coupling and cyclization by means of a Hoppe’s homoaldol reaction and a Mukaiyama–Michael-type addition, respectively. Furthermore, we showcase how the orchestrated combination of an asymmetric Michael addition, a tandem oxidation–aldol reaction and a pinacol rearrangement can dramatically improve the efficiency in synthesizing gelsedine-type alkaloids, with nary a protecting group. Finally, to address the supply issue of several drugs, including anti-influenza drug zanamivir and antitumor agent Et-743, we exploit scalable and practical approaches to provide advantages over current routes in terms of cost, ease of execution, and efficiency.

Organic Sonochemistry: A Chemist’s Timely Perspective on Mechanisms and Reactivity

“…When seeking a mechanistic rationale, a convenient approach is the elucidation of convergent and divergent processes (Scheme ). , This view on reactivity envisages the plausibility of competitive, simultaneous polar and radical pathways. When silent and ultrasonic reactions converge to the same product(s), only an overall acceleration usually results from sonication along with a different product distribution.…”

A Sustainable Synthesis of the SARS-CoV-2 Mpro Inhibitor Nirmatrelvir, the Active Ingredient in Paxlovid

“…13 The strategy selected for the synthesis of nirmatrelvir, therefore, focused on the inherent benefits on scale of a convergent route. 14 Moreover, it seemed advantageous to perform our Pd-catalyzed amide dehydration 15 in this convergent fashion, as subsequent steps provide opportunities to limit the amount of residual Pd in the final API.…”

An Environmentally Responsible Synthesis of the SARS-CoV-2 Mpro Inhibitor Nirmatrelvir (PF‑07321332), the Active Ingredient in Paxlovid

“…The strategy selected for the synthesis of nirmatrelvir focused on the inherent benefits of convergent syntheses on scale. 13 Additionally, it was advantageous to perform our Pd-catalyzed amide dehydration in this convergent fashion, as subsequent steps provide opportunities to limit the amount of residual Pd in the final product.…”