E/Z Photoisomerization of Olefins as an Emergent Strategy for the Control of Stereodivergence in Catalysis

Abstract

The stereoselective photoisomerization of olefins via Energy Transfer (EnT) sensitization bears significant potential in the context of rational design of catalytic stereodivergent methodologies. Whereas approaches for controlling the access to E‐ and Z‐ isomers depend highly on the nature of the catalyst – and therefore are not easily implemented as a general strategy – EnT catalysis has emerged in recent years as an increasingly powerful tool for olefin geometry control in a nearly perfect step‐economic fashion. Moreover, this approach presents both high functional group tolerance and, most notably, has demonstrated ample multicatalytic compatibility. This feature has enabled the development of tandem stereodivergent catalytic strategies, which are the focus of this Review.

Merging Grubbs second-generation catalyst with photocatalysis enablesZ-selective metathesis of olefins: scope, limitations, and mechanism

“…Importantly, PCa and PCf–PCh possessing higher triplet energies gave decent Z : E ratios (80 : 20 to 90 : 10). 7 These results are in good accordance with Zhang's report that cyanoarenes are competent catalysts for stilbene photoisomerization. 14 The low Z : E ratio obtained when riboflavin (PCb, entry 2) is used as a photocatalyst is obviously due to its low solubility in dichloromethane.…”

“…Based on the ability of visible light photocatalysis to promote E → Z isomerization of olefins, 7 as demonstrated by the seminal works of Weaver, 8 Gilmour 9 and many others, 10 we reasoned that the combination of this approach with standard ruthenium-based metathesis catalysts would provide practically simple one-pot access to Z -olefins. However, the feasibility of this dual catalytic (Ru/PC) system depends on the compatibility of the metathesis catalysts as well as the different intermediates generated during the metathesis process with the photocatalytic conditions ( Scheme 1C ).…”

Regio- and Stereoselective Electrochemical Alkylation of Morita–Baylis–Hillman Adducts

“…Interestingly, 3aa was recovered in 95% yield as a 1:1.7 E / Z mixture, showing the intrinsic unsuitability of some photocatalytic methodologies aiming at the stereoselective formation of α-substituted cinnamates. 19 …”

“…1:1). , To prove a possible photomediated isomerization of the final cinnamyl C–C double bond, we subjected ( E )- 3aa ( E / Z > 20:1) to visible-light irradiation in the presence of a common triplet-emitter Ir-based photosensitizer (Ir­[dF­(CF 3 )­ppy] 2 (dtbppy)­PF 6 , (1 mol %, Scheme b). Interestingly, 3aa was recovered in 95% yield as a 1:1.7 E / Z mixture, showing the intrinsic unsuitability of some photocatalytic methodologies aiming at the stereoselective formation of α-substituted cinnamates …”

“…Interestingly, 3aa was recovered in 95% yield as a 1:1.7 E/ Z mixture, showing the intrinsic unsuitability of some photocatalytic methodologies aiming at the stereoselective formation of α-substituted cinnamates. 19 Mechanistically, the eChem cycle depicted in Scheme 4 is tentatively proposed. This starts with the cathodic fragmentation of 2a into CO 2 , phthalimide anion, and the desired cyclohexyl radical.…”