A single precatalyst tandem RCM–allylic oxidation sequence

Abstract

Ring closing metathesis of allyloxy styrenes and a subsequent Ru-catalyzed allylic oxidation can be combined to a tandem sequence that makes coumarins accessible using less active but more conveniently available first generation catalysts.

Cyclization of ortho-hydroxycinnamates to coumarins under mild conditions: A nucleophilic organocatalysis approach

“…Recent new methodologies based on CH-activation reactions still use acidic reaction media and show, in part, a lack of regioselectivity [7–10]. Such problems may be circumvented by using ring-closing metathesis [11–12] or other approaches [13–15]. In selective synthetic schemes, the generation of coumarins is typically realized by the cyclization of ortho -hydroxycinnamates (Scheme 1).…”

Recent Advancements in Stereoselective Olefin Metathesis Using Ruthenium Catalysts

“…CM promoted by 1 followed by dihydroxylation using NaIO4 as an oxidant delivered diol products through rutheniumcatalyzed dihydroxylation. The ruthenium alkylidene functioned as the oxidation catalyst in the presence of NaIO4 [167][168][169][170][171][172]. Dihydroxylation is a stereospecific process, and because the metathesis was under thermodynamic control, the E-olefin was formed in excess leading to syn-diols.…”

“…Assisted tandem catalysis is a method that employs a single catalyst to perform multiple transformations. Ruthenium metathesis catalysts have been utilized in transformations as C-C bond forming agents that can promote additional structural elaborations [162][163][164][165][166][167][168]. CM promoted by 1 followed by dihydroxylation using NaIO4 as an oxidant delivered diol products through rutheniumcatalyzed dihydroxylation.…”

Tandem Olefin Metathesis/Oxidative Cyclization: Synthesis of Tetrahydrofuran Diols from Simple Olefins

“…11 While the precise nature of the oxidized ruthenium species has not been firmly established, if this species is also capable of catalyzing oxidative cyclization, then 1,5-dienes accessible via olefin metathesis could be transformed into 2,5-disubstituted THF diols in a stereocontrolled fashion (Figure 2B). …”

“…Given the activity of cyclometalated alkylidene Ru-5 in the oxidative cyclization of 1 (Table 1), and the use of Ru-5 in tandem Z -selective cross metathesis–dihydroxylation, 11d we anticipated that this complex would also be able to catalyze the oxidative cyclization of Z -diene intermediates in a stereospecific fashion. Using Ru-5 as catalyst, diene 5a and 5g underwent cross metathesis with an excess of allyl benzoate (5 equiv), to give an E,Z -diene intermediate, which then underwent oxidative cyclization upon exposure to the oxidative conditions to provide diol 6l and 6m in 45% and 30% yield, 21 respectively (Scheme 2).…”