It was a great pleasure to discuss many new and very ‘distant’ subjects with Dr. Ing. Alessandro Bramanti and with the NNL team in Bari, now involved in the European project MolarNET. Ferrocenyl alcohols and many chemicals were a precious gift from Johnson Matthey Catalysis. I give my keenest acknowledgments for a very generous supply of ferrocene derivatives to Antonio Zanotti-Gerosa, a world leader in stereoselective hydrogenation, but principally a very good friend. I am grateful to my outstanding colleagues and friends in the Ciamician Department for helpful discussions. I am also extremely grateful for very fruitful talks with Herbert Mayr. I would like to acknowledge Claire Margaret Wilson for proofreading this document. I have briefly mentioned the students involved in the project and their practical and intellectual contributions – again, thanks to all of you!
Abstract
Diastereoselective SN 1-type reactions have been known for many years and have been used in the synthesis of many natural products. It has recently been shown that chiral nucleophiles, obtained using organocatalytic methodologies, can react with highly reactive carbenium ions in a stereoselective fashion. Based on this, carbenium ions can be applied in asymmetric catalytic reactions.
1 Introduction
1.1 Reaction of Ferrocenyl Alcohols with Lewis Acids
2 Reaction of Alcohols ‘on Water’
2.1 Stability of Carbenium Ions and the Mayr Scale
3 Organocatalytic Stereoselective SN 1-Type Reactions of Aldehydes and Isolated Carbenium Ions
3.1 Attempts at the Related Asymmetric SN 1-Type α-Alkylation of Ketones
3.2 Organocatalytic Stereoselective SN 1-Type Reactions under Oxidative Conditions
4 Organocatalytic SN 1-Type Reactions Involving Lewis Acids
5 Alkylation of Aldehydes Made Simple with the Benzodithiolylium Ion
6 Organocatalytic SN 1-Type Reactions Involving Brønsted Acids
7 SN 1-Type Reactions Promoted by Chiral Thioureas
8 Conclusion and Perspectives
Key words organocatalysis - S
N 1-type reactions - carbenium ions - alkylations - stereoselectivity