1.Tuning the Chirality of Block Copolymers: From Twisted Morphologies to Nanospheres by Self-Assembly.
Suárez-Suárez S1, Carriedo GA1, Presa Soto A2. Chemistry. 2015 Sep 28;21(40):14129-39. doi: 10.1002/chem.201501705. Epub 2015 Aug 11.
New advances into the chirality effect in the self-assembly of block copolymers (BCPs) have been achieved by tuning the helicity of the chiral-core-forming blocks. The chiral BCPs {[N=P(R)-O2C20H12](200-x)[N=P(OC5H4N)2](x)}-b-[N=PMePh]50 ((R)-O2C20H12 = (R)-1,1'-binaphthyl-2,2'-dioxy, OC5H4N = 4-pyridinoxy (OPy); x = 10, 30, 60, 100 for 3 a-d, respectively), in which the [N=P(OPy)2] units are randomly distributed within the chiral block, have been synthesised. The chiroptical properties of the BCPs ([α]D vs. T and CD) demonstrated that the helicity of the BCP chains may be simply controlled by the relative proportion of the chiral and achiral (i.e., [N=P(R)-O2C20H12] and [N=P(OPy)2], respectively) units. Thus, although 3 a only contained only 5% [N=P(OPy)2] units and exhibited a preferential helical sense, 3 d with 50% of this unit adopted non-preferred helical conformations. This gradual variation of the helicity allowed us to examine the chirality effect on the self-assembly of chiral and helical BCPs (i.
2.Ligand-promoted oxidative cross-coupling of aryl boronic acids and aryl silanes by palladium catalysis.
Yu J1, Liu J, Shi G, Shao C, Zhang Y. Angew Chem Int Ed Engl. 2015 Mar 23;54(13):4079-82. doi: 10.1002/anie.201412288. Epub 2015 Feb 3.
The first cross-coupling reaction between aryl silanes and aryl boronic acids is described. This transformation represents one of the very few examples of coupling reactions between two nucleophilic organometallic reagents and provides a new method for the formation of biaryl compounds. The successful development of this reaction was enabled by the use of commercially available 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) as the ligand. A small amount of BINAP (3 mol %) was sufficient to suppress the formation of the homocoupling products, and the reaction yielded the cross-coupling products with high selectivity under mild conditions, even when the ratio of the two coupling partners was 1:1.
3.Chiral 2 + 3 Keto-Enamine Pseudocyclophanes Derived from 1,3,5-Triformylphloroglucinol.
Kieryk P1, Janczak J2, Panek J1, Miklitz M1, Lisowski J1. Org Lett. 2016 Jan 4;18(1):12-5. doi: 10.1021/acs.orglett.5b02989. Epub 2015 Dec 14.
The reactions of 1,3,5-triformylphloroglucinol with (1R,2R)-1,2-diaminocyclohexane, (1R,2R)-1,2-diphenylethylenediamine, or (R)-2,2'-diamino-1,1'-binaphthyl result in the formation of enantiopure [2 + 3] keto-enamine condensation products, in contrast to analogous reactions of 1,3,5-triformylbenzene, where [4 + 6] Schiff base cages are formed. The X-ray crystal structure of the diaminocyclohexane 2 + 3 derivative as well as modeled structures of other compounds of this type show cyclophane-like molecules with close contact between the phloroglucinol rings. Density Functional Theory (DFT) calculations confirm that there is a sizable π-π interaction between these rings influencing the conformation of these molecules.
4.Diastereomeric preference of a triply axial chiral binaphthyl based molecule: a concentration dependent study by chiroptical spectroscopies.
Dezhahang Z1, Poopari MR, Hernández FE, Diaz C, Xu Y. Phys Chem Chem Phys. 2014 Jul 7;16(25):12959-67. doi: 10.1039/c4cp01704h.
We have examined the effects of environmental perturbations, specifically solvents and concentrations, on axial chirality of a recently synthesized axially chiral binaphthyl fluorene based salen ligand, named AFX-155, . Chirality and dominant conformations of AFX-155 in CDCl3 solvent have been characterized using vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy in combination with DFT calculations. AFX-155 exhibits triple axial chirality: one is at the binaphthyl ring and the other two are related to the axes of chirality along the -C-N bonds where Cs are part of the binaphthyl group. To evaluate solvent and concentration dependence, complementary VA and VCD experiments in both THF-d8 and CDCl3 have been performed, as well as the optical rotatory dispersion (ORD) and electronic CD (ECD) measurements in CDCl3 under much diluted conditions.