Catalyst‐Controlled Stereoselective Barton–Kellogg Olefination

Abstract

Overcrowded alkenes are expeditiously prepared by the versatile Barton–Kellogg olefination and have remarkable applications as functional molecules owing to their unique stereochemical features. The induced stereodynamics thereby enable the controlled motion of molecular switches and motors, while the high configurational stability prevents undesired isomeric scrambling. Bistricyclic aromatic enes are prototypical overcrowded alkenes with outstanding stereochemical properties, but their stereocontrolled preparation was thus far only feasible in stereospecific reactions and with chiral auxiliaries. Herein we report that direct catalyst control is achieved by a stereoselective Barton–Kellogg olefination with enantio‐ and diastereocontrol for various bistricyclic aromatic enes. Using Rh2(S‐PTAD)4 as catalyst, several diazo compounds were selectively coupled with a thioketone to give one of the four anti‐folded overcrowded alkene stereoisomers upon reduction. Complete stereodivergence was reached by catalyst control in combination with distinct thiirane reductions to provide all four stereoisomers with e.r. values of up to 99:1. We envision that this strategy will enable the synthesis of topologically unique overcrowded alkenes for functional materials, catalysis, energy‐ and electron transfer, and bioactive compounds.

Asymmetric Catalytic (2+1) Cycloaddition of Thioketones to Synthesize Tetrasubstituted Thiiranes

“…The elaborations of some enantioenriched thiiranes were also carried out. Unfortunately, it was found that tetrasubstituted alkenes D1 – D4 via desulfuration of thiirane C1 or C33 , namely Barton–Kellogg olefination, [4c, 14] were afforded in decent results under varied conditions (Scheme 2c, see the Supporting Information for details). These results indicate that the high tense strain of the 3‐membered ring of thiirane was more likely to be released via desulfuration, [4c, 6] rather than substitution reaction, ring opening or expansion [15] .…”

“…Unfortunately, it was found that tetrasubstituted alkenes D1 – D4 via desulfuration of thiirane C1 or C33 , namely Barton–Kellogg olefination, [4c, 14] were afforded in decent results under varied conditions (Scheme 2c, see the Supporting Information for details). These results indicate that the high tense strain of the 3‐membered ring of thiirane was more likely to be released via desulfuration, [4c, 6] rather than substitution reaction, ring opening or expansion [15] . Of note, the tetrasubstituted olefins D3 and D4 were obtained in high E / Z selectivity when thiirane C33 with high diastereoselectivity was employed [16] .…”

“…A representative example of the catalytic enantioselective thionation of epoxides was reported by List group, [4a,b] in which racemic epoxides were converted into enantioenriched epoxides and thiiranes in the presence of a highly efficient chiral TRIP catalyst (Scheme 1b). Recently, the Sparr group reported a stereoselective Barton–Kellogg olefination via a chiral Rh II complex‐catalyzed thiiranation (Scheme 1c) [4c] . As such, the assembly of multi‐substituted enantioenriched thiiranes is still a particularly challenging area, even with stoichiometric amounts of enantioenriched materials [1, 3]…”

Novel Copper(II) Complexes with Dipinodiazafluorene Ligands: Synthesis, Structure, Magnetic and Catalytic Properties

“…Certain derivatives of 4,5-diazafluorene belong to the group of the so-called bistricyclic aromatic enes (BAEs). BAEs and related polycyclic systems are a class of molecular materials that display a rich variety of conformations, dynamic stereochemistry and switchable chirality, color, and spectroscopic properties [43][44][45]. The chelating fragment of 4,5-diazafluorene incorporated into an overcrowded alkene molecule leads to new, unusual properties of the transition metal complexes [42,46].…”

Synthesis of cis-thiiranes as diastereoselective access to epoxide congeners via 4π-electrocyclization of thiocarbonyl ylides

“…Alternatively, the episulfidation of alkenes has been investigated 15 , but this seemingly straightforward epoxidation-like approach is applicable only to a limited range of cyclic alkenes. Otherwise, stereoselective synthesis of thiiranes has rarely been developed [41][42][43][44][45] , and most of the reported examples have serious drawbacks such as low stereoselectivity, narrow substrate scope, and/ or the requirement of highly toxic reagents. Among these precedents, a unique synthetic sequence of the Barton-Kellogg reaction is noteworthy (Fig.…”