Synthesis of the ABCDEF-ring of ciguatoxin 3C

Eight-Membered Rings With One Oxygen Atom

“…A wide range of natural products bearing an oxocane or oxocene unit were synthesized through RCM approach to obtain their eightmembered heterocycle precursor namely in the synthesis of subunit B of PbTx-1 2, 103 subunits B and F of PbTx-1 2, 104 subunit H of PbTx-2 3, 105,106 subunit B 0 of MTX-1 22, 107,108 subunit G of YTX 26, [108][109][110] subunit E of CTX-3C 15, 111,112 oxocane unit in the total In addition, RCM and other different strategies for the total synthesis of the eight-membered core of heliannuols A 43, K 109 and L 115 have been reviewed by Chen et al 129 Another important aspect to refer is that Shishido group has assigned in 2005 benzoxocane structures for heliannuols G 107 and H 108 and in 2006 revised them to substituted dihydrobenzofurans 107a and 108a, respectively, with an external trans-olefin intact. 130 Using Grubbs I catalyst 84, 2-(but-3-en-1-yl)-1-(prop-2-en-1-yloxy)benzenes in dichloromethane at room temperature under argon atmosphere gave 5,6-dihydro-2H-benzo[b]oxocines 131 ; while under refluxing conditions and nitrogen atmosphere 7-(but-3en-1-yloxy)-8-(prop-2-en-1-yl)flavones gave a couple of oxocine-fused flavones 132 and 3-(but-3-en-1-yloxy)-2-(prop-2-en-1-yl) pyran in argon atmosphere afforded pyran-fused oxocene.…”

Synthesis of the MN Ring of Caribbean Ciguatoxin C-CTX-1 via Desymmetrization by Acetal Formation

“…Having synthesized the M ring, we moved on to the synthesis of the MN ring (Scheme ). Protection of diol 2 as bis-TES ether 14 (90%) followed by regioselective Swern oxidation , furnished aldehyde 15 (78%). HWE reaction with phosphonate 16 under Masamune–Roush conditions afforded enone 17 (94%).…”