This paper describes the synthesis of (+)-allopumiliotoxin 323B' (1) using the intramolecular [3 + 2]-cycloaddition reaction of the (Z)-N-alkenylnitrone 4. This synthesis began with (R)-tert-butyl-3-hydroxy-pent-4-enoate [(R)-13] which was obtained by enzymatic resolution with Amano PS lipase. A series of manipulations gave intermediate 17 and in situ coupling with 4-benzoyloxybutanal lead to the (Z)-N-alkenylnitrone 4 which underwent an intramolecular [3 + 2]-cycloaddition reaction to give the isoxazolidine 3 as the major cycloadduct. Isoxazolidine 3 provided the piperidinone 24 which upon diastereofacial selective addition of MeMgBr gave the required tertiary alcohol 25. Formation of the indolizidine core 2 was achieved by an intramolecular S(N)2 reaction. The side chain was assembled from a Wittig reaction between the phosphorane 8 and the enantiomerically pure aldehyde 9. Further modifications afforded the aldehyde 7 which underwent an aldol condensation with the potassium enolate of the indolizidone core 2. Dehydration gave the enone 37 which was converted into the anti-diol 38 by intramolecular hydride reduction. Finally, deprotection of the BOM protecting group gave (+)-allopumiliotoxin 323B' (1).

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Selective Fluorination of Alkyl C-H Bonds via Photocatalysis. -The work presents a novel method to generate N-radicals via triplet-triplet energy transfer catalyzed by anthraquinone. Due to the involvement of these cationic radicals in hydrogen abstraction the reaction is selective for electron rich sp 3 C-H bonds. -(KEE, C. W.; CHIN, K. F.; WONG, M. W.; TAN*, C.-H.; Chem. Commun. (Cambridge) 50 (2014) 60, 8211-8214, http://dx.doi.org/10.1039/c4cc01848f ; Div. Chem. Biol. Chem., Nanyang Technol. Univ., Singapore 637616, Singapore; Eng.) -M. Paetzel 51-043

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