P-19 不斉四級炭素構築法の開発と天然物合成への応用(ポスター発表の部)

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Two novel methods for the construction of asymmetric quaternary carbon centers, which were frequently found in biologically active natural products, have been developed. These methodologies feature the utilization of a readily accessible tertiary asymmetric carbon centers for the assembly of requisite asymmetric quaternary carbon center. Additionally, the application of these to natural products synthesis has been demonstrated. 1. Construction of a Benzylic Quaternary Asymmetric Carbon Center via [1,5]C-H Insertion Reaction of Alkylidene Carbene and Fomal Total Synthesis of (-)-α-Cuparenone Heck reaction of p-iodotoluene with 2-'butyl-4,7-dihydro-1,3-dioxepine 6 gave the acetal 7, which was sequentially ozonized and reduced with NaBH_4 to afford the 2-aryl-1,3-propanediol 8 in good overall yield. Asymmetric acetylation of 8 with PPL in the presence of vinyl acetate provided the monoacetate 9 with R configuration in excellent chemical and optical yield. Conversion of 9 to the TMS acetylene derivative 13 by a standard manipulation followed by treatment of alkynyl iodonium salt 14, which was derived from 13, with sodium benzenesulfinate in water at 0℃ produced the cyclopentenyl sulfone 16, via the [1,5]C-H insertion reaction of the transient alkylidene carbene 15, with configuration retention at the benzylic quaternary carbon center in 82% yield from 13. The sulfone 16 was led to the enone 18 in 2 steps, which had been successfully converted to (-)-α-cuparenone 19. 2. Construction of a Quaternary Asymmetric Carbon Center via 1,4-Asymmetric Induction During Intramolecular [3+2] Dipolar Cycloaddition Reaction and its Application Intramolecular [3+2] dipolar cycloaddition of the optically active nitrile oxides, 33 and 50, which were generated from the oximes, 32 and 49, by oxidation with NaOCl, produced diastereoselectively the cycloadducts 34_a and 51_a, respectively. These structures were determined by ^1HNMR and n.O.e. experiments. The former adducts 34_a was then transformed to the crutial intermediate for the synthesis of antiulcer natural product cassiol 41. On the other hand, the latter 51_a was converted to the A-ring synthon of abietanoid diterpene pygmaeocin B 53.
天然有機化合物討論会の論文
1995-09-01

P-19 不斉四級炭素構築法の開発と天然物合成への応用(ポスター発表の部)

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