Amidyls in radical cascades. The total synthesis of (±)-aspidospermidine and (±)-13-deoxyserratine

Total Synthesis and Stereochemical Assignment of (–)-Zenkequinone B

“…Pleasingly, this one-pot reaction proceeded cleanly to afford (±)-zenkequinone B (1) in 85% yield. The spectroscopic data of the synthetic material were in good agreement with the natural product in all aspects, and thus, we have accomplished the shortest total synthesis of (±)-zenkequinone B (1) 10,11 in 68% overall yield from the known enyne 16 14 (Scheme 2).…”

“…As shown in Scheme 2, our synthesis of (±)-zenkequinone B (1) commenced with the addition of allylmagnesium bromide to ketone 15 to furnish enyne 16 14 which was then refluxed with Grubbs' first-generation catalyst ( 17) 15 to generate the diene 18 in 80% yield. Having synthesized diene in good quantity, the final and key one-pot Diels-Alder reaction of diene 18 with 1,4-naphthoquinone 12 followed by aerobic oxidative aromatization with silica gel and Et 3 N was attempted.…”

Some aspects of radical cascade and relay reactions

“…As part of our research programme related to the development of new, practical methods for the generation of nitrogen-centred radicals [14], we devised sequences allowing the construction of the pyrrolizidine and indolizidine backbones 3 and 5 found in many alkaloid families, as well as the rarer perhydroazaazulene structure 7 present in certain natural substances such as the stemona alkaloids [15]. Our approach, which relies on our development of hydroxamate esters as convenient sources of amidyl radicals, is summarized in scheme 1.…”

“…Extending the side-chain by one more carbon whilst keeping the chlorine, as in 1 (n = 2; X = Cl), results in the formation of perhydroazaazulenone 7 through a 7-endo closure and Scheme 1. General routes to pyrrolizidines, indolizidines and perhydroazaazulenes [15]. Scheme 2.…”

Some aspects of radical chemistry in the assembly of complex molecular architectures

“…Outlined in Scheme 2 is a very short total synthesis of (±)-13-deoxyserratine ( 11 ) [12–13]. The first two of the four rings in 11 are again created through the powerful Pauson–Khand reaction starting from trivial enyne 5 and oxidation of the protected alcohol in the side-chain of cyclopentenone 6 directly into carboxylic acid 7 by using Jones’ reagent.…”