Herbert Brown

Asymmetric Synthesis Based on Borane Intermediates


Abstract

It is a rare experience to have had the opportunity to carry out research on a selected topic for 60 years. Research normally proceeds at a slow pace. Day by day and week by week it is difficult to see much progress. But research is cumulative. Each discovery makes possible advances in many areas.

On my graduation from the University of Chicago in 1936, my classmate, Sarah Baylen, gave me a graduation gift, a copy of “The Hydrides of Boron and Silicon” by Alfred Stock (Karlsruhe). This book persuaded me to do my Ph.D., with Professor H. I. Schlesinger and Dr. A. B. Burg, exploring the chemistry of diborane.

Why did Sarah select this book out of the hundred of chemistry books available in the University of Chicago bookstore? 1936 was the height of the Great Depression. Both of us had lost our fathers at an early age. We were both very poor. She selected as her present the cheapest chemistry book in the bookstore!

The Ph. D. study of the reaction of diborane with aldehydes and ketones opened up the hydride era of organic reductions. The study of this reaction led to the discovery of alkali metal borohydrides. Study of the reducing characteristics of the borohydrides led to the discovery of hydroboration. Hydroboration provided a simple synthetic route to organoboranes. Investigation established that these compounds have a most versatile chemistry. This study provided in 1961 the first non-enzymatic asymmetric synthesis in high ee and opened this new active research area to chemists. Clearly, we had discovered a Major New Continent of Chemistry.

Some recent developments, to be discussed, reveal that we have not yet completed the exploration. It will require a new generation of chemists to continue this exploration and apply the riches of the New Continent for the good of Mankind.

1.Beginnings
2.Volatile Compounds of Uranium
3.Alkali Metal Route to Diborane
4.Alkali Metal Borohydrides
5.Selective Reductions
6.Hydroborations
7.Versatile Organoboranes
8.Asymmetric Hydroboration
9.Asymmetric Synthesis Made Easy
10.a-Pinene: Superior Chiral Auxiliary
11.Asymmetric Reductions
12.Asymmetric Allyl- and Crotylboration
13.Asymmetric Opening of Meso Epoxides
14.Asymmetric Enolborations


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