Selective Functionalization of Achmatowicz Rearrangement Products by Reactions with Potassium Organotrifluoroborates under Transition-Metal-Free Conditions

Abstract

The repertoire of synthetic transformations of the products of the Achmatowicz rearrangement has been expanded by exploring their reactivity with potassium organotrifluoroborates in the absence of transition metals. Depending on the reaction conditions and the substitution pattern of the starting material, the reaction may lead to the stereoselective synthesis of dihydropyranones (2,6- trans), tetrahydropyranones (2,3- cis-2,6- cis) or functionalized 1,4-dicarbonyl compounds. The method has also been adapted for the one-pot synthesis of functionalized pyrroles.

Achmatowicz Rearrangement-Inspired Development of Green Chemistry, Organic Methodology, and Total Synthesis of Natural Products

“…Notably, it has been demonstrated that enantiomerically pure dihydropyranones can be obtained from the corresponding optically active furylcarbinols without any loss of optical purity. Additionally, many efficient transformations of AchR products (Scheme ), such as (1) reductive etherification, (2) Ferrier-type allylation, (3) spiroketalization, (4) molybdenum complexation as chiral scaffolds (Liebeskind et al), (5) palladium-catalyzed O -glycosylation (O’Doherty et al; Feringa et al), (6) dynamic kinetic isomerization (Tang et al), (7) alkenylation, (8) in situ generation of 3-oxidopyridilium ion for [5 + 2] cycloaddition, and (9) Hoffmann rearrangement to cyclopentenones, have been established as a reliable way to obtain fully functionalized pyrans/cyclopentenones. The related aza-version of AchR was realized successfully to provide functionalized piperidinones/piperidines .…”

C-Aryl Glycosylation: Palladium-Catalyzed Aryl–Allyl Coupling of Achmatowicz Rearrangement Products with Arylboronic Acids

“…It was found that all phosphine-containing palladium precatalysts examined proved to be ineffective (Table , entries 1–4). It should be noted that O’Doherty used Pd 2 (dba) 3 –CHCl 3 /PPh 3 (1/2.5 ratio) for the related O-glycosylation and the catalytic system did not work for our arylation. Fortunately, we found that the phosphine-free PdCl 2 (entry 5) and Pd­(OAc) 2 (entry 6) did catalyze the arylation but with only 15 and 49% yields, respectively.…”

“…These results conclusively suggested that the C4-keto group of glycosyl donors played a key role in the palladium-catalyzed reaction: it either greatly assisted the formation of the Pd π-allyl complex or substantially enhanced the electrophilic reactivity of the Pd π-allyl complex. To explore the direct Ferrier-type arylation of 1a and 3a with arylboronic acid through an oxonium ion intermediate, we performed another controlled experiment that employed Brønsted (TFA) or Lewis acids (TMSOTf and FeCl 3 ) to activate 1a and 3a (Scheme b). No desired 2aa or 4a products were detected, while significant decomposition was observed.…”

“…Encouraged by our previous work on Pd-catalyzed arylation of aza-Achmatowicz products with arylboronic acids, we strongly believed that the corresponding arylation of Achmatowicz products with arylboronic acids would be highly viable . Although such arylation has not been reported, alcohols and 1,3-dicarbonyls were successfully used for Pd-catalyzed Tsuji–Trost-type O -glycosylation and [3 + 2] cycloaddition, respectively (Scheme ).…”

Photoinduced Vicinal 1,2-Difunctionalization of Olefins for the Synthesis of Alkyl Sulfonamides

“…Therefore, organotrifluoroborates were selected as nontraditional carbon-based nucleophiles because of their commercial availability, ease of synthesis, and wide variety. These moieties have previously been shown to possess nucleophilic character; however, except for our previous work, these reactions generally require the use of strong Brønsted or Lewis acids, limiting the functional group tolerance of these methods. − As a whole, this area of chemistry has largely been underexplored.…”