Employing a chiral spirodiphosphine monoxide ligand with 1,1'-spirobiindane backbone (SDP(O)), a desymmetrization strategy of Pd-catalyzed intramolecular asymmetric aryl C-O coupling of 2-(2-halophenoxy)propane-1,3-diols, was developed. The SDP(O) ligand shows much better results than its SDP counterpart. The protocol provides an efficient and highly enantioselective method for the synthesis of 2-hydroxymethyl-1,4-benzodioxanes. Density functional theory studies provide a model that accounts for the origin of the enantioselectivity.
We propose a series of modified methods covering timing and frequency synchronization in the coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) system. The modified timing synchronization method eliminates the ambiguity of Park's method, and the modified frequency synchronization method employs only one training symbol without any loss of accuracy compared to Schmidl's method. The proposed synchronization scheme is tested in a 20 Gb∕s CO-OFDM simulated system, with the result that the modified synchronization scheme gives a more accurate timing estimation and a more economical frequency offset estimation with a wide estimation range in the relatively short transmission distance. Meanwhile, chromatic dispersion compensation added before the synchronization keeps the modified scheme's performance stable over longer distances and makes better subcarrier recovery with the optical signal-to-noise ratio improved by 3 dB at the bit-error rate of 10 −3 .
The differentiation of two nucleophilic amide groups in malonamides through a copper-catalyzed enantioselective intramolecular aryl C-N coupling reaction is demonstrated based on an asymmetric desymmetrization strategy. Such a method afforded enantioenriched 2-oxo-1,2,3,4-tetrahydroquinoline-3-carboxamides in high yields and moderate to good enantioselectivity.
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