Prevost reaction synthesis

Polyhalo ketones, reductive dehalogenation of, 29, 2 Pomeranz-Fritsch reaction, 6, 4 Prevost reaction, 9, 5 Pschorr synthesis, 2, 6 9, 7 Pnmmerer reaction, 40, 3 Pyrazolines, intermediates in diazoacetic ester reactions, 18, 3 Pyridininm chlorochromate, 53, 1 Pyrolysis ... 

The Prevost Reaction allows the synthesis of anti-diols from alkenes by the addition of iodine followed by nucleophilic displacement with benzoate in the absence of water. Hydrolysis of the intermediate diester gives the desired diol.The Woodward Modification of the Prevost Reaction gives syn-diols. 

The total synthesis of (-)-SS20846A, a 2-alkyl-4-hydroxypiperidine natural product exhibiting antibacterial and anticonvulsant properties, was achieved by C.R. Johnson and co-workers. The key transformations included an alkene metathesis for the preparation of the piperidine ring and the Prevost reaction for the installation of the 4-hydroxy substituent. 

The Markownikov addition of the elements of water to a cleavamine derivative may also have important application in the synthesis of bisindole alkaloids. Although this appears not to have been achieved, a route to the corresponding derivative of catharanthine has been developed, by use of a modified Prevost reaction. Thus, treatment of catharanthine with iodine and silver acetate in glacial acetic acid afforded an intermediate, which was reduced to the acetate (223) by NaBH4. Although formulated otherwise this acetate must be the 20a -acetate, by reason of its later conversion into vinblastine (q.v.). 

Recently, Vidari et al. synthesized 9-deoxygelsemide (75), which was isolated earlier from Gelsemium elegans by Takayama et al. [104, 105]. The key synthetic steps were the variant Woodward-Prevost reaction for installation of characteristic cis-a-l,2-dioxygenated system at C-6 and C-7, and construction of the dihydropyran ring via formylation of y-lactone. The total synthesis of the iridoid was achieved in 11 steps and 6.6% overall yield from enantiomerically pure lactone (76) (Scheme 97.5). 

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