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Originally reported in Liebigs Annalen in 1953 (then called Justus Liebigs Annalen der Chemie), the Wittig reaction has evolved to include the Horner–Wittig and Horner–Wadsworth–Emmons reactions and several other variations. Today, these reactions constitute some of the most powerful processes for the construction of carbon–carbon bond frameworks, facilitating the chemical synthesis of myriads of organic molecules both in research laboratories and industrial settings. The Wittig and related reactions were proven particularly useful in the field of total synthesis, where they enabled the construction of highly complex structures and had a significant impact in shaping the art to its present state of sophistication. In this article the authors focus, after a brief introduction, on total syntheses from their own laboratories that employ such processes. These examples, together with the numerous others adorning the chemical literature, illustrate amply the importance of the Wittig and related reactions and point to their continuing prominence in organic synthesis.

The Wittig and Related Reactions in Natural Product Synthesis

The advent of organic synthesis and the understanding of the molecule as they occurred in the nineteenth century and were refined in the twentieth century constitute two of the most profound scientific developments of all time. These discoveries set in motion a revolution that shaped the landscape of the molecular sciences and changed the world. Organic synthesis played a major role in this revolution through its ability to construct the molecules of the living world and others like them whose primary element is carbon. Although the early beginnings of organic synthesis came about serendipitously, organic chemists quickly recognized its potential and moved decisively to advance and exploit it in myriad ways for the benefit of mankind. Indeed, from the early days of the synthesis of urea and the construction of the first carbon–carbon bond, the art of organic synthesis improved to impressively high levels of sophistication. Through its practice, today chemists can synthesize organic molecules—natural and designed—of all types of structural motifs and for all intents and purposes. The endeavor of constructing natural products—the organic molecules of nature—is justly called both a creative art and an exact science. Often called simply total synthesis, the replication of nature's molecules in the laboratory reflects and symbolizes the state of the art of synthesis in general. In the last few decades a surge in total synthesis endeavors around the world led to a remarkable collection of achievements that covers a wide ranging landscape of molecular complexity and diversity. In this article, we present highlights of some of our contributions in the field of total synthesis of natural products of biological and medicinal importance. For perspective, we also provide a listing of selected examples of additional natural products synthesized in other laboratories around the world over the last few years.

Constructing molecular complexity and diversity: total synthesis of natural products of biological and medicinal importance

The second generation strategy for the total synthesis of brevetoxin B (1) is presented. According to this •strategy, the heptacyclic (ABCDEFG) phosphonium iodide 4 and the tricyclic (UK) aldehyde 3 were defined as the precursors for the brevetoxin B skeleton. The Yamaguchi lactonization was successfully applied for the formation of the (EFG) and (DEFG) lactones (15 -* 7) and (29 6), respectively. The required appendage on ring (E) was efficiently introduced via a Murai coupling, involving addition of a higher order organocuprate derived from iodide 20 to the lactone-derived enol triflate 16 (16 — 25). The minor epimer of the resulting product 6fi was then converted to the desired isomer 6 a via hydrogenation using an Ir(I) catalyst. A number of approaches were considered for further elaboration of lactone 6. Among them a convienient Cr/Ni-promoted coupling' reaction was developed and applied to the introduction of the side chain on ring D. The scope and generality of this reaction was examined with a variety of aldehydes (e.g., 39, 59, and 62). Construction of 38 was thus achieved from vinyl triflate 36 and the ring B aldehyde 39. However, the projected intramolecular Michael addition (41 — ■ 1 42) and reductive hydroxy ketone cyclization (47 48) failed to yield ring C. Fetizon cyclization afforded the pentacyclic lactone (CDEFG) (51 — * 52), which resisted further useful functionalization, Using the more elaborate aldehyde 62, the Cr/Ni coupling reaction afforded allylic alcohol 64, which then served as a precursor to the pentacyclic lactol 80. The latter compound also resisted advancement to more elaborate intermediates, leading to abandonment of this approach and the formulation of a new strategy.

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Total Synthesis of Brevetoxin-B .2. 2nd Generation Strategies and Construction of the Dioxepane Region [Defg]

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Total Synthesis of Brevetoxin-B .2. 2nd Generation Strategies and Construction of the Dioxepane Region [Defg]