- The iso-VAPOL ligand: Synthesis, solid-state structure and its evaluation as a BOROX catalyst
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The new vaulted biaryl ligand iso-VAPOL is an isomer of VAPOL but has the chiral pocket of VANOL. The synthesis of iso-VAPOL involves a cycloaddition/electrocyclization cascade (CAEC) similar to one that is used for VAPOL except that the starting material
- Gupta, Anil K.,Zhang, Xin,Staples, Richard J.,Wulff, William D.
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p. 4406 - 4415
(2015/02/02)
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- Synthesis, resolution, and determination of absolute configuration of a vaulted 2,2′-binaphthol and a vaulted 3,3′-biphenanthrol (VAPOL)
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Two methods for the synthesis of vaulted biaryls were developed involving the reactions of carbene complexes with alkynes and the [2 + 2] cycloaddition of ketenes. The final step in the synthesis of 3,3′-diphenyl-[2,2′-binaphthalene]-1,1′-diol (39) and 2,2′-diphenyl-[3,3′-biphenanthrene]-4,4′-diol (47) (VAPOL) was phenol coupling of the 3-phenyl-1-naphthol (14) and the 2-phenyl-4-phenanthrol (28), respectively. The naphthol 14 could be prepared from the thermolysis of phenylacetyl chloride in the presence of phenylacetylene or from the benzannulation of the pentacarbonyl(phenylmethoxymethylene)chromium(0) (15) with phenylacetylene which upon an acetylative workup gives O-acetyl-4-methoxy-2-phenyl-1-naphthol (16). The reductive cleavage of the acetoxy group in 16 was unexpectedly affected by aluminum chloride and ethanethiol which were used to cleave the methyl ether. In a similar manner, the phenanthrol 28 could either be prepared from the 1-naphthylacetyl chloride (30) or pentacarbonyl-(1-naphthylmethoxymethylene)chromium(0) (21). A new procedure for the preparation of carbene complexes was developed utilizing dimethyl sulfate as methylating agent. Unlike the benzannulation of the phenyl complex 15, the benzannulation of the naphthylcarbene complex 21 with phenylacetylene gave a side product which resulted from the incorporation of 2 equiv of the alkyne. This side product could be minimized by the proper control of the concentration of the alkyne. The phenol coupling of the 3-phenyl-1-naphthol with ferric chloride gave 2,2′-diphenyl-[2,2′-binaphthalene]-4,4′-diol (38) and with air as oxidant gave the of 3,3′-diphenyl-[2,2′-binaphthalene]-1,1′-diol (39). Oxidative coupling of the 2-phenyl-4-phenanthrol (28) with air gave 2,2′-diphenyl-[3,3′-biphenanthrene]-4,4′-diol (47) (VAPOL), but the same coupling with 2-tert-butyl-4-phenanthrol (34) failed. The 2,2′-binaphthol 39 was resolved via its cyclic diester with phosphoric acid by salt formation with (-)-brucine, and the 3,3′-biphenanthrol 47 was resolved via its cyclic deiester with phosphoric acid (49) by salt formation with (-)-cinchonidine. The configuration of (-)-39 was shown to be S from an X-ray analysis of the brucine salt, and the configuration of (+)-47 was shown to be S from an X-ray analysis the amide (S,S)-54 derived from 49 and (S)-α-methylbenzylamine.
- Bao, Jianming,Wulff, William D.,Dominy, James B.,Fumo, Michael J.,Grant, Eugene B.,Rob, Alexander C.,Whitcomb, Mark C.,Yeung, Siu-Man,Ostrander, Robert L.,Rheingold, Arnold L.
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p. 3392 - 3405
(2007/10/03)
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