Highly Enantioselective Synthesis of Cyclic Aminals with a Cyclopentadiene‐Based Chiral Carboxylic Acid

Abstract

A highly enantioselective aminalization of 2‐aminobenzenesulfonamides and aldehydes catalyzed by a novel cyclopentadiene‐based chiral carboxylic acid has been realized. The cost‐effective and readily synthesized cyclopentadiene‐based chiral carboxylic acid was found to be a highly reactive Brønsted acid for this transformation, affording benzothiadiazine class of cyclic aminals with up to 98 % ee.

Enantioselective PCCP Brønsted acid-catalyzed aminalization of aldehydes

“…Due to the high stability of the aromatic cyclopentadienyl anion, PCCPs exhibit a low pK a value comparable to that of phosphoric acids. Contrary to chiral phosphoric acids, PCCPs offer less laborious and inexpensive prepa- ration protocols [31,32], which makes them an interesting alternative for chiral Brønsted acid-catalyzed transformations [30][31][32][33][34][35].…”

Iridium‐Catalyzed ortho‐C−H Amidation of Benzenesulfonamides with Sulfonyl Azides

“…Specifically, 2-aminobenzenesulfonamides act as a key precursor for the synthesis of benzothiadiazine 1,1-dioxides. [8] Classic methods for the synthesis of 2aminobenzenesulfonamides include sequential chlorosulfonylation of aromatic amine and ammonolysis with chlorosulfonic acid [9] and the reaction of aromatic amine with chlorosulfonyl isocyanate followed by cyclization of the resulting chlorosulfonylureas with Lewis acids. [10] Although these methods are efficient and reliable, they still suffer from several disadvantages such as harsh reaction conditions, moisture sensitivity, narrow scope of substrates, and isomer formation.…”

“…Notably, amidation does not take place when AgSbF 6 is used as silver salt (Table 1, entry 7). In additon, only moderate yields were obtained by employing AgOTf and AgTFA as silver salts(Table 1, entries8,9). Remarkably, the Ag 2 CO 3 showed excellent activity and gave 92% yield (Table 1, entry 10).…”

Synthesis of 1,2,3,4,5‐Penta(methoxycarbonyl)cyclopentadienides through Electrocyclic Ring Closure and Ring Contraction Reactions

“…Recently, Lambert et al developed a novel highly efficient type of chiral Brønsted acid catalyst, which is easily derived from PMCP. Although the new platform first showed efficiency for specific examples of Mukaiyama–Mannich and oxocarbenium aldol reactions (the substrates must have a 2‐hydroxyphenyl substituent for good association with it) it was later extended to asymmetric Diels–Alder cycloaddition reactions and synthesis of chiral cyclic aminals . PMCP was used in the transfer hydrogenation of quinolines; asymmetric hydrogenation was also investigated .…”