Diastereoselective deprotonative metalation of chiral ferrocene derived acetals and esters using mixed lithium-cadmium and lithium-zinc combinations

International audienceIn situ bimetal combinations, and notably those prepared from MCl2(radical dotTMEDA) (M=Zn, Cd; TMEDA=N,N,N′,N′-tetramethylethylenediamine) and Li(TMP) (3 or 4 equiv, TMP=2,2,6,6-tetramethylpiperidino), were screened for their ability to diastereoselectively deprotonate ferrocenes bearing a chiral group. The ferrocene carboxylate generated from diacetone-d-glucose afforded the corresponding 2-iodo derivative in 74% yield with 90% de (SP diastereoisomer) using the base generated from CdCl2 and Li(TMP) (3 equiv), and in 85% yield with 91% de (SP diastereoisomer) through a double asymmetric induction using a chiral lithium-zinc base generated from ZnCl2*TMEDA and lithium (R)-bis(1-phenylethyl)amide (4 equiv). In contrast, using a combination prepared from ZnCl2 and Li(TMP) (4 equiv) with the ferrocene carboxylate obtained from 6-(tert-butoxycarbonylamino)-6-deoxy-3-O-methyl-1,2-O-isopropylidene-α-d-glucofuranose led to the RP-iodo derivative in 57% yield after separation. Suzuki coupling was performed satisfactorily on the isolated SP and RP diastereoisomer iodoesters

Synthesis of both enantiomers of ferrocene[1,2-c]1H-quinolin-2-one by diastereoselective deproto-zincation of sugar-derived ferrocene esters

This research has also been performed as part of the Indo-French "Joint Laboratory for Sustainable Chemistry at Interfaces". The calculations were performed by using the RIKEN Integrated Cluster of Clusters (RICC) facility.International audienceDiastereoselective deproto-metallation of several sugar-derived ferrocene esters using lithium-zinc bases was studied. While bis[(R)-1-phenylethyl]amino as ligand afforded the diacetone-D-glucose-based (SP)-2-iodoferrocene ester in 91% de after iodination, the RP was synthesized from α-D-glucofuranose using 2,2,6,6-tetramethylpiperidino as ligand. Both (RP)- and (SP)-ferrocene[1,2-c]1H-quinolin-2-one were reached by subsequent cyclizing coupling, albeit their racemization was noted

Photometry and Polarimetry of 2010 XC15_{15}: Observational Confirmation of E-type Near-Earth Asteroid Pair

Asteroid systems such as binaries and pairs are indicative of physical properties and dynamical histories of the Small Solar System Bodies. Although numerous observational and theoretical studies have been carried out, the formation mechanism of asteroid pairs is still unclear, especially for near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric and polarimetric observations of a small NEA 2010 XC$_{15}$ in 2022 December to investigate its surface properties. The rotation period of 2010 XC$_{15}$ is possibly a few to several dozen hours and color indices of 2010 XC$_{15}$ are derived as $g-r=0.435\pm0.008$, $r-i=0.158\pm0.017$, and $r-z=0.186\pm0.009$ in the Pan-STARRS system. The linear polarization degrees of 2010 XC$_{15}$ are a few percent at the phase angle range of 58$^{\circ}$ to 114$^{\circ}$. We found that 2010 XC$_{15}$ is a rare E-type NEA on the basis of its photometric and polarimetric properties. Taking the similarity of not only physical properties but also dynamical integrals and the rarity of E-type NEAs into account, we suppose that 2010 XC$_{15}$ and 1998 WT$_{24}$ are of common origin (i.e., asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair ever confirmed, possibly formed by rotational fission. We conjecture that the parent body of 2010 XC$_{15}$ and 1998 WT$_{24}$ was transported from the main-belt through the $\nu_6$ resonance or Hungaria region.Comment: Resubmitted to AAS Journals. Any comments are welcom

Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications

Organomagnesium compounds, representated by the Grignard reagents, are one of the most classical yet versatile carbanion species which have widely been utilized in synthetic chemistry. These reagents are typically prepared via oxidative addition of organic halides to magnesium metals, via halogen-magnesium exchange between halo(hetero)arenes and organomagnesium reagents or via deprotonative magnesiation of prefunctionalized (hetero)arenes. On the other hands, recent studies have demonstrated that the organo-alkaline earth metal complexes including those based on heavier alkaline earth metals such as calcium, strontium and barium could be generated from readily available non-polar unsaturated molecules such as alkenes, alkynes, 1,3-enynes and arenes through unique metallation processes. Nonetheless, the resulting organo-alkaline earth metal complexes could be further functionalized with variety of electrophiles in various reaction modes. Especially, organocalcium, -strontium and barium species have shown unprecedented reactivity in the downstream functionalization, which could not be observed in the reactivity of organomagnesium complexes. This perspective will focus on the newly emerging protocols for the generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their applications in chemical synthesis and catalysis.Ministry of Education (MOE)Nanyang Technological UniversityPublished versionThis work was supported by funding from the Nanyang Technological University (NTU) and the Singapore Ministry of Education (Academic Research Fund Tier 2: MOE2019-T2-1-089) (for S. C.) as well as JSPS KAKENHI grant JP19K06992 (for R. T.)