In -pseudopterosin-A synthesi

The oxidative formation of p-benzoquinones from anilides such as 7-108 was used for the synthesis of the core scaffold of the natural products elisabethin A (7-106) and pseudopterosin A aglycone (7-107) (Scheme 7.30). Exposure of anilide 7-108 to DMP [53] led to the formation of the o-imidoquinone 7-109, which underwent an intramolecular Diels-Alder reaction to give 7-110 in 28% yield after hydration. In a competitive pathway, the p-quinone 7-111 is also formed from 7-108, which on heating in toluene again underwent an intramolecular Diels-Alder reaction to give cycloadduct 7-112 in 25% overall yield. Hydrolysis of 7-112 furnished the carbocyclic skeleton 7-113 of elisabethin A (7-106). 

Epoxy-ene cyclizations have been used as key steps in natural products synthesis. The preparations of pseudopterosin, a potent antiflammatory agent and analgesic <88JOCl584>, and (+)-aphidicolin <85TL6147,88JOC4929), (+ )-9,10-jyn- and (+)-9,10-an/i-copalol <92JOC4598> are representative examples of the synthetic utility of Lewis acid-catalyzed epoxide cyclizations. 

In a series of publications, Nicolaou and coworkers have demonstrated the utility of DMP for the selective oxidation of 4-substituted anilides 894 to p-quinones 895 and 2-substituted anilides 896 to < -azaquinones 897 (Scheme 3.360) [1289-1291], The first process was applied to the short, efficient total synthesis of epoxyquinomycin B [1290], while the second type of oxidation allowed rapid access to complex analogs of pseudopterosin and elisabethin natural products [1291],... 

Although many notable examples of nickel-catalyzed hydrovinylations have been described, their iterative use in the synthesis of the pseudopterosins provides a clear demonstration of the utility of this strategy (Scheme 3-94). In this impressive illustration, three sequential ligand-controlled hydrovinylation processes enable a highly efficient synthesis of the target molecule. 

Corey et al. reported a successful total synthesis of pseudopterosin E (116) through a crucial coupling reaction of 2-0-benzyl-3,4-di-0-p-methoxybenzoyl-a-L-fucosyl bromide (115) and catechol 114 the fucosylation of 114 with 115 proceeded in the complete position-selective and a-stereoselective manner, providing exclusively a-fucoside 116 (Scheme 20), and the a-stereoselectivity of the reaction was ascribed to the internal 1,4-remote participation of the p-methox-ybenzoyl group (Fig. 9) [72],... 

Majdalani, A. and Schmalz, H.G. (1997) Chiral ti -arene-Cr(CO) complexes in organic syntiiesis a short and highly selective synthesis of the 18-nor-seco-pseudopterosin aglycone. Tetrahedron Lett., 38, 4545-4548. 

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