# Titanium cis‐DACH Salan Catalyst for the Efficient Epoxidation of Nonactivated Olefins with Hydrogen Peroxide‐Terminal‐Selective Epoxidation of Multiply Unsaturated Terpenes

## TL;DR

A new titanium catalyst efficiently epoxidizes nonactivated olefins using hydrogen peroxide, with high regioselectivity for terminal double bonds in complex terpenes.

## Contribution

A novel titanium salan catalyst with pentafluorophenyl substituents enables efficient and selective epoxidation of nonactivated olefins and multiply unsaturated terpenes.

## Key findings

- The catalyst achieves up to 95% yield at 0.5 mol-% loading for epoxidation of nonactivated olefins.
- It shows high regioselectivity (up to 49:1) for terminal double bond epoxidation in multiply unsaturated terpenes.
- Syn/anti selectivity of up to 9:1 is observed in the epoxidation of chiral substrates like (S)-citronellene and (R)-linalool.

## Abstract

We report a new generation of highly active and readily available homogeneous titanium catalysts for the epoxidation of nonactivated olefins with aqueous hydrogen peroxide. Key feature is the introduction of pentafluorophenyl substituents into a salan ligand derived from cis‐1,2‐diaminocyclohexane (cis‐DACH). Our novel salan ligand is accessible in one single step by reductive alkylation of cis‐DACH with 3‐(pentafluorophenyl)salicylic aldehyde. In situ complexation with Ti(OiPr)4 of the cis‐DACH salan provides the titanium catalyst, which, in the presence of aqueous hydrogen peroxide, smoothly epoxidizes a broad spectrum of olefins with up to 95% yield at a catalyst loading of 0.5 mol‐% only. The achiral cis‐DACH salan catalyst showed syn‐selectivity (4.7:1) in the epoxidation of a chiral, racemic terminal allylic alcohol. This catalyst furthermore allows the regioselective (up to 49:1) epoxidation of the terminal double bond in multiply unsaturated terpenes such as myrcene, (S)‐citronellene, and (R)‐linalool. For the latter two substrates, syn/anti‐selectivity of up to 9:1 was observed. Augmented syn/anti selectivity (up to 50:1 syn or 25:1 anti) can be induced in the epoxidation of the chiral substrates (S)‐citronellene and (R)‐linalool when the “matched” enantiomer of the chiral “Berkessel salalen ligand” is employed.

Terminal‐selective epoxidation–catalytic, simple, and with H2O2 as oxidant. The titanium complex of a new type of salan ligand, accessible in one step from cis‐DACH and 3‐(pentafluorophenyl)salicylic aldehyde, is an efficient catalyst for the epoxidation of nonconjugated olefins with H2O2. Most importantly, the novel catalyst is highly regioselective for terminal double bond epoxidation when multiply unsaturated substrates are employed.