Photochemical Behavior of Doubly Bridged Dewar Benzenes – Synthesis of Prismanes

Abstract

In this paper we report on the photochemistry of Dewar benzenes bridged at the 1,4‐ and 5,6‐positions and substituted at the 2,3‐positions. It was found that simple alkyl substitution leads to prismanes only to a minor extent. Introduction of phenyl groups into the 2‐ or 2,3‐positions gives the corresponding doubly bridged prismanes in yields up to 80% Pentamethylene‐bridged bis‐Dewar benzenes 19 rearrange upon irradiation to 22. Irradiation of the doubly bridged Dewar benzene derivatives with one ester group at the 5‐position does not yield isolable products. However, introduction of one tert‐butylsulfonyl group such as 30–33 gives almost quantitative yields of isolable prismanes if pentamethylene or hexamethylene bridges are used. The nonbridged species, 2‐tert‐butylsulfonyl‐1,4,5,6‐tetramethylbicyclo[2.2.0]hexa‐2,5‐diene (44), aromatizes upon irradiation into 1‐(tert‐butylsulfonyl)‐2,3,4,5‐tetramethylbenzene (45). In contrast to the pentamethylene‐bridged monosulfone 47, the corresponding disulfone 38 undergoes no photochemical reaction. This could be explained by the X‐ray structure, which reveals a strong interaction between one of the tert‐butyl groups and the pentamethylene chain bridging the double bond in 38.

Classic Annulenes, Nonclassical Applications

“…Quite spectacularly, when neat samples of 15 are irradiated with 365 nm light, photoisomerization is followed by rapid crystal formation. Monitoring this process by 1 H NMR confirmed that the photoisomerization was indeed quantitative and gave no signs of byproducts such as prismane . All things considered, Dewar benzene 15 is an ideal example of a supramolecular protecting group for synthon 16 .…”

“…Monitoring this process by 1 H NMR confirmed that the photoisomerization was indeed quantitative and gave no signs of byproducts such as prismane. 38 All things considered, Dewar benzene 15 is an ideal example of a supramolecular protecting group for synthon 16. Specifically, the protecting group eradicates the aryl moiety, thus inhibiting intermolecular arylaryl interactions that would otherwise promote crystallization.…”

Copper-Catalyzed Disulfonation of Terminal Alkynes with Sodium Arylsulfinates

“…Among them, 1,2-disulfonylethenes are considerable organosulfone molecules , and emerge as versatile synthons in synthetic applications such as cycloaddition, radical elimination, and 1,2-rearrangement reaction . To date, several classic methods including oxidation, condensation, and addition reactions were well established for the production of the 1,2-disulfonylethenes. However, these approaches are always restricted to predecorated feedstocks, narrow substrate scopes, and/or multiple synthetic steps.…”

In Quest of a Prismene. Organolithium-Induced Desulfonylation on Strained Hydrocarbons

“…An appropriate compound which was easily accessible was 8 (see Scheme 1). 6 We have therefore investigated the sulfinate elimination for 8 as well as for 11 and 14, both of which are readily available via a Diels-Alder reaction 7 and subsequent light induced [2 + 2] cycloaddition (Scheme 2). This assumption seemed reasonable because similar bridgehead olefins have been shown to be intermediates in other reactions, in which they were trapped by anthracene and furane derivatives.…”