Synthesis of (−)-halichonic acid and (−)-halichonic acid B

• Keith P. Reber and
• Emma L. Niner

Beilstein J. Org. Chem. 2022, 18, 1629–1635, doi:10.3762/bjoc.18.174

• (−)-α-bisabolol. The optimized synthetic route includes a new purification method for isolating (−)-7-amino-7,8-dihydrobisabolene in enantiomerically pure form via recrystallization of its benzamide derivative. The key intramolecular aza-Prins reaction forms the characteristic 3-azabicyclo[3.3.1]nonane

• acids. Keywords: alkaloid; amino acid; aza-Prins reaction; cascade reaction; natural product; Introduction Marine sponges produce a large number of structurally diverse natural products, including many that exhibit biological activity [1][2][3]. In 2019, Tsukamoto and co-workers isolated the

• configuration was not rigorously established, we have assigned it as the (E)-isomer, as is commonly observed in aldimine formation. The stage was now set for the key intramolecular aza-Prins reaction that would form the bicyclic structures of the halichonic acids (Scheme 2). When a solution of imine 7 in

Prins fluorination cyclisations: Preparation of 4-fluoro-pyran and -piperidine heterocycles

• Guillaume G. Launay,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2010, 6, No. 41, doi:10.3762/bjoc.6.41

• methodology was extended to the aza-Prins reaction using N-tosyl-homoallylic amines to generate the corresponding 4-fluoropyrrolidines. In general, these reactions leading to both the 4-fluorotetrahydropyrans and 4-fluoro-pyrrolidines occur with good to high conversions, however the diastereoselectivities are

• in the products, differing only in the orientation of the fluorine. In general, these reactions gave good diastereoselectivities in moderate to good yields (Scheme 3). Aza-Prins fluorination reaction The aza-Prins reaction is less well known but has been exploited, e.g., in tandem reactions in

• -1-ol (3) (1 equiv), aldehyde (1 equiv), DCM, −20 °C, 5 h. Prins reactions using vinylcyclohexanol 8 and an aldehyde at −20 °C. Reaction conditions: BF3·OEt2 (1 equiv), 2-vinylcyclohexanol (8) (1 equiv), aldehyde (1 equiv), DCM, −20 °C, 5 h. Aza-Prins reaction between N-homoallyl-N-tosylamine (13