Catalytic Asymmetric Iodoesterification of Simple Alkenes

Catalytic asymmetric iodoesterification of simple alkenes was achieved using a dinuclear zinc‐3,3′‐(R,S,S)‐bis(aminoimino)binaphthoxide ( di‐Zn ) complex. For iodoesterification using p‐methoxybenzoic acid, the N‐iodonaphthalenimide (NIN)‐I₂ system was effective for producing iodoesters in a highly enantioselective manner. The synthetic utility of chiral iodo‐p‐methoxybenzoates was also demonstrated. The quartet of metal ionic bond, hydrogen bond, halogen bond, and π‐π stacking is harmonized on the single reaction sphere of di‐Zn catalyst for enabling the highly enantioselective catalytic asymmetric iodoesterification of simple alkenes for the first time.     

Structural and thermodynamic aspects of ionic solvation in concentrated aqueous poly(ethylene glycol)

Solvation of ions in concentrated aqueous poly(ethylene glycol) (PEG) has been studied from thermodynamic and structural viewpoints using ion-transfer voltammetry at the interface between aqueous and nitrobenzene phases and X-ray absorption fine structure (XAFS). Systematic changes in the ion-transfer potential from water to aqueous PEG have been confirmed for several ions relative to the corresponding potential of tetraethylammonium ion (Et4N+), which is almost independent of PEG concentration. The results obtained for alkali cations strongly suggest the involvement of their complexation with PEG even in relatively diluted PEG solutions. It has been implied that the solvation circumstances of Br- and ClO4- are drastically altered when the PEG concentration becomes higher than particular critical values (e.g., 30-50% PEG200), where free water molecules are diminished because of the hydration of PEG. XAFS measurements have also been performed for K+ and Br- to get direct evidence for these findings. Although the spectra at the K K-edge clearly indicate the presence of a PEG complex of K+ in relatively diluted PEG solutions ( approximately 33% PEG200), an obvious increase in its ion-transfer potential has been detected at lower PEG concentrations, indicating that complexes formed at the interface rather than in bulk solution are transferred into an organic phase. Br- is fully hydrated in 0-50% PEG solutions, whereas some water molecules are replaced by PEG when the PEG concentration increases. Increasing the PEG concentration causes decreases in the coordination number from 6 in water to 2-3 in neat PEG. Thus, the present approach not only has elucidated the structural and thermodynamic aspects of ionic solvation in aqueous PEG but also has provided the information of the hydration of PEG.     

Formal Synthesis of Olivacine via Indolylborate

Palladium‐catalyzed tandem cyclization–cross‐coupling reaction of indolylborate 2 and vinyl bromide 5 was successfully applied in a short formal synthesis of olivacine. The reaction of 2 with 5 in the presence of Pd(OAc)₂ readily afforded three kinds of products, triene derivative 6 and vinylindole derivative 7 , along with a small amount of the piperidine derivative 8 (Scheme 2). On the other hand, the reactions of 2 with bromide 10 or 15 were also examined (Schemes 4 and 5), and their outcome markedly depended on the relative ease of ring closure as a function of ring size. Irradiation of 6 with a high‐pressure mercury lamp (→ 9 ; Scheme 2), followed by removal of the N‐[(benzyloxy)carbonyl] group and subsequent oxidation afforded, after deprotection, pyridocarbazole 23 , and the conversion of 23 to olivacine is known (Scheme 6).     

Formal Total Synthesis of Fostriecin by 1,4‐Asymmetric Induction with an Alkyne–Cobalt Complex

The synthesis of a protected dephosphofostriecin, and thereby a formal synthesis of fostriecin, has been accomplished. The synthetic challenges were the construction of four stereogenic centers and the conformationally labile cis‐cis‐trans‐triene moiety. Previous total syntheses have employed at least two asymmetric reactions that required the use of an external chiral auxiliary. Although remote stereoinduction in a 1,4‐relationship is considered difficult, we have developed a notable 1,4‐asymmetric induction that utilizes an alkyne–cobalt complex for the control of C5 stereochemistry by the C8 stereogenic center. The stereochemistry at C11 was established by 1,3‐asymmetric induction with a higher‐order alkynyl‐zinc reagent. Thus, only one asymmetric reaction requiring an external chiral auxiliary was employed in this route. The labile cis‐cis‐trans‐triene unit was constructed at a late stage of the synthesis by diastereoselective coupling of a dienyne and an aldehyde unit, followed by reduction.     

A facile method for generation of carbon oxide sulfide

Carbon oxide sulfide was easily generated upon heating of amine salts of carbamothioic acids at 85°C which were produced in situ from amines, carbon monoxide, and elemental sulfur in the presence of a catalytic amount of selenium under mild conditions.