At a meeting of the Faculty of Arts and Sciences on Feb. 6, 2024, the following tribute to the life and service of the late David Albert Evans was spread upon the permanent records of the Faculty.
David Albert Evans was one of the most influential organic chemists in the history of the field, and his impact was felt through his research, mentorship, and teaching. He discovered practical and general ways to synthesize polyketides, a broad class of medicinally important natural products. To crack this problem, he devised exquisitely simple yet broadly effective reagents and catalysts. The pinnacle of that effort was the Evans aldol reaction, a synthetic method that permanently altered the course of the field. Evans mentored generations of outstanding scientists and revolutionized the way organic chemistry is taught in the classroom.
Evans was born in Washington, D.C., and was raised in Fairfax County, Virginia. His father, Albert, died when Evans was only 16. His mother, Iris, his younger brother, Thomas, and Evans moved to Iris’s hometown of Williamsport, Pennsylvania, where Evans graduated from Williamsport High School in 1959. Evans and Selena Anne “Sally” Welliver were the only two from their high school class going to Oberlin College, so he dared to ask her out on a date. They were married in 1962. Sally remained Evans’s closest friend and companion throughout his life. They graduated in 1963 with bachelor’s degrees in chemistry. Evans earned his Ph.D. at the California Institute of Technology in 1967 and began his independent academic career at the University of California, Los Angeles, that same year. Sally and Evans’s daughter, Bethan, was born in 1971.
Evans returned to Caltech as a full professor in 1974 and was ultimately recruited to Harvard in 1983. He was appointed as the Abbott and James Lawrence Professor of Chemistry in 1990 and served as chairman of the Department of Chemistry and Chemical Biology from 1995 to 1998.
Natural products synthesis motivated Evans’s research, and, like others in the field, he selected his targets based on their biological activity and the structural challenges they presented. What distinguished his work was his commitment to devising the ultimate total synthesis. There is a right way to make a molecule, he would say, and that synthesis should stand the test of time. Such thinking usually required the development of new chemical reactions. Breakthroughs from the first phase of his career include advances in organosilicon and organosulfur chemistry, the development of new sigmatropic rearrangements, and the discovery of new concepts in hydride reduction.
But there was a holy grail in the field of organic synthesis on which Evans had set his sights: control over the stereochemical outcome of the aldol reaction. The Nobel laureate John Cornforth had articulated the importance of the challenge in 1975, “Nature, it seems, is an organic chemist having some predilection for the aldol and related condensations.” For human organic chemists to synthesize many of the most important and biologically active natural products the “right way,” they needed a way to control the stereochemistry of the aldol reaction.
Evans proposed a solution to his student Javier Bartrolí, sketching it on a sheet of paper that Javi proudly preserved and revealed 40 years later at a symposium celebrating Evans’s 80th birthday. Through ingenious design of chiral auxiliaries that could be attached temporarily to one of the reacting partners in the aldol, Evans envisioned that high selectivity should be achievable. The idea worked almost precisely as he had predicted. Such rational design of new reactions is exceedingly rare, even today. “Evans auxiliaries” forever redefined the way chemists approach the challenges of asymmetric synthesis. The Evans Group applied them in an assortment of now-classic total syntheses. Countless more applications of the Evans aldol ensue continuously in academic laboratories and the pharmaceutical industry.
The later phase of Evans’s research career was distinguished both by astonishing achievements in total synthesis and by his dramatically successful entry into the field of asymmetric catalysis. His group introduced a new class of chiral ligands for reactive metals called bis(oxazolines) (or BOX ligands) that, like his earlier chiral auxiliaries, are beautifully simple yet broadly effective. They applied the BOX ligands to a dazzling array of metal-catalyzed reactions that enabled numerous beautiful syntheses. These ligands are applied to cutting-edge problems in chemical selectivity to this day.
Evans also transformed organic chemistry through innovations in technology and teaching. Organic chemists think and communicate with chemical line drawings, which, until the mid-1980s, had to be rendered tediously by hand or with stencils. Evans conceived of a user-friendly chemical structure drawing program and, together with a graduate student, Stewart Rubenstein, and Evans’s wife, Sally, developed ChemDraw. The software was announced in 1985 and rapidly became, and remains, an indispensable tool for organic chemists.
Evans was dedicated to education. He created and perfected Chemistry 206, a course in advanced organic chemistry that provided a new intellectual framework for the field and influenced how similar classes are taught worldwide. He made his lecture notes and problem banks freely available, and today every advanced organic chemistry course has Chem 206 deep in its DNA.
At Harvard, Evans’s lab became the definitive training ground for future leaders in organic chemistry. The list of extraordinary scientists who worked with Evans includes a 2021 Nobel Prize in Chemistry winner and many of the field’s current thought leaders. Evans’s impact as a teacher and mentor was simply immense.
Evans espoused a rigorous way of thinking about reactivity and selectivity that drew directly from fundamental principles. He would never hesitate to challenge students, seminar speakers, or younger colleagues to “go to the board.” Even if the target of attention became paralyzed with nervousness, Evans would masterfully walk them toward a deep insight into the chemistry in question. The whole audience would be transformed by Evans’s chemical intuition and acumen.
Finally, it is important to recognize both the deep sense of adventure that Evans and Sally shared and the intrinsic sense of generosity they exuded. In their boat, they explored the seacoast, harbors, storms, and the splendid nature from Cape Cod throughout New England to Nova Scotia. These qualities were the hallmarks of their relationships with students, faculty, and families of the department.
James G. Anderson
Eric Jacobsen, Chair