An Ireland–Claisen rearrangement/RCM based approach for the construction of the EF-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.…”

A New Variant of Fused Cyclic Ether Synthesis Based on Ireland-Claisen Rearrangement and RCM

“…The process employed (Z)-3-alkoxyprop-2-en-1-yl glycolate esters having a cyclic ether on the C2 oxygen of the glycolate moiety (1) as substrates for the Ireland-Claisen rearrangement, and the substrates stereoselectively rearranged to ,-dialkoxyesters (3), which were successfully transformed to fused cyclic ethers (4) by a sequence of steps including RCM. The process was successfully applied to the construction of the EF-ring of ciguatoxin 3C [10].…”