Resolution of a Configurationally Stable Hetero[4]helicene

Abstract

We have developed an efficient chemical resolution of racemic hydroxy substituted dithia-aza[4]helicenes (DTA[4]H) 1(OH) using enantiopure acids as resolving agents. The better diastereomeric separation was achieved on esters prepared with (1S)-(−)-camphanic acid. Subsequent simple manipulations produced highly optically pure (≥ 99% enantiomeric excess) (P) and (M)-1(OH) in good yields. The role of the position where the chiral auxiliary is inserted (cape- vs bay-zone) and the structure of the enantiopure acid used on successful resolution are discussed.

Efficient Spin-Selective Electron Transport at Low Voltages of Thia-Bridged Triarylamine Hetero[4]helicenes Chemisorbed Monolayer

“…≥99%. The absolute configuration of the single enantiomers of derivatives HelSAc was assigned as ( P )-(+) and ( M )-(−) by comparison with our previous results on helicenes of type HelSAc . − Additional details about the synthesis can be found in the Supporting Information (Figure S1 to Figure S4).…”

A Lewis Base Hydrogen Bond Donor (LB/HBD) Organocatalytic Approach to Dithiabridged Triarylamine Hetero[4]helicenes

“…Thus, we decided to verify whether this new methodology could be exploited for the control of the absolute stereochemistry of helicenes 1 using enantiopure LBs. Several helicenes 1 have been resolved by HPLC, [3,5,9,10] and for specific derivatives a chemical resolution was also possible [17] . However, the possibility of running enantioselective synthesis of helical shaped compounds is a challenging goal.…”

“…Several helicenes 1 have been resolved by HPLC, [3,5,9,10] and for specific derivatives a chemical resolution was also possible. [17] However, the possibility of running enantioselective synthesis of helical shaped compounds is a challenging goal. [18] Phenothiazine 2 a was used as model substrate and enantiopure selenium substituted LBs 4 h-j, and sulfur substituted LBs (R)-5 g, and 5 h-m (Figure 3) were selected by their availability among the classes of chalcogen derivatives that ensured a complete and fast conversion (see Table 1).…”

Strongly reducing helical phenothiazines as recyclable organophotoredox catalysts

“…We initially synthesized a series of phenothiazine catalysts ( PTHS 1–3 ) that were obtained in short steps and a moderate yield using commercially available starting materials to probe the relationship between their structure and physical properties (Table 1). 11,12 Interestingly, we found that these catalysts have low excited-state oxidation potentials ( E 1/2 ox * = −2.34 to −2.40 V vs. SCE) compared to other phenothiazine catalysts such as PTH 1–4 . Therefore, PTHS 1–3 were expected to reduce various substrates via oxidative quenching cycles.…”