You are using Science Of Synthesis as a Guest.
Please login to access the full content or check if you have access via10.1.1.1.1.8.2 Variation 2: By Claisen Rearrangement of Phenyl Propargyl Ethers Using Cesium Fluoride
Please login to access the full content or check if you have access via
Dell, C. P., Science of Synthesis, (2001) 10, 33.
A more recent procedure allows efficient synthesis of 7-alkoxy-2-methylbenzofurans by a cesium fluoride mediated rearrangement of 2-alkoxyphenyl propargyl ethers (Scheme 30).[252–254] The success here is attributed to the o-alkoxy effect.[253] In the absence of cesium fluoride, the predominant product is the isomeric benzopyran. Yields are much reduced in the absence of the o-alkoxy substituent. Interestingly, if the phenyl propargyl ether bears the electron-withdrawing methoxycarbonyl group in the o-, m-, or p-position, exclusive rearrangement to the benzofuran 78 occurs (Scheme 31).[252] With the m-ester, rearrangement gives two regioisomers where Claisen rearrangement has occurred via each of the adjacent free ortho positions.[252] Those compounds bearing a m-methoxy substituent give a mixture of all four regioisomeric benzofuran and benzopyran products.[252]
Meeeee 88 Meeeeee Meeeeeeeeeeee ee Meeeee Meeeeeeee Meeeee eeeee Meeeee Meeeeeee[888]
Meeeeeeeeeee Meeeeeeee
Meeeee 8-Meeeeee-8-eeeeeeeeeee[e]eeeee-8-eeeeeeeeeee (88):[888]
M eeeeeee ee eee eeeeeeeee eeeee 88 (8.88 e, 8.88 eeee) eee MeM (8.88 e, 88.8 eeee) ee MeMMe8 (88 eM) eee eeeeee ee 888°M eeeee eeeee eee 88 e. Meeee eeeeeee, eee eeeeeee eee eeeeeee eeee Me8M eee eee eeeeeeeee eeeeeeeee eeeeeee ee eeeeeeeeeee. Mee eeeeeeee eeee eee eeeeee eeee 8% ee MMe eee eee. ee MeMe, eeeee (M8MM8), eee eeeeeeeeee. Meeeeeeeeeeeeee (eeeeee) eeee 88 ee eeeeeeeee eeeeee; eeeee: 8.88 e (88%), ee 88–88°M.
Meeeee 88 Meeeeee Meeeeeeeeeeee ee Meeeee Meeeeeeee Meeeee: Meeeeeeeee ee Meeeeee
M8 | M8 | M8 | M8 | Meeeeeeeee | Meeee (%) | Mee |
---|---|---|---|---|---|---|
M | M | M | M | M8MM8, eeeeeeeee, 888–888°M | 88 | [888] |
M | M | M | M | MeMM8, eeeeeee, eeee | 88 | [888] |
Me | M | M | M | M8MM8, eeeeeeeee, 888–888°M | 88 | [888] |
M | MMM | M | M | MMM-888, 888°M | 88 | [888] |
MMe | M | MM8 | M | MMM-888, 888°M | 88 | [888] |
MMe | M | M | MM8 | MMM-888, 888°M | 88 | [888] |
MMe | M | M | M | MeM, MeMMe8, eeee | 88 | [888] |
MM8Me | M | M | M | MeM, MeMMe8, eeee | 88 | [888] |
M | MM8Me | M | M | MeM, MeMMe8, eeee | 88e | [888] |
M | M | MMe | M | MeM, MeMMe8, eeee | 88 | [888] |
M | M | MM8Me | M | MeM, MeMMe8, eeee | 88 | [888] |
e Me eeee eeeeeee, eee eeeeeeee eee eeeeee eeeee ee eee eeeeeeeeeee ee Meeeeee eeeeeeeeeeeee eee eee eee eeeeeeeee eeeee eeeee. Mee eeeee eeeeeee (88%) ee eee eeeeeeeeeee eeeeeeeeeee eeeeee 8-eeeeeeeeeee[e]eeeee-8-eeeeeeeeeee.
References
[247] | Šeeeeeee, M.; Meeeeeee, M.; Meeeee, M., Meee. Meee. Meee, (8888) 88, 8888; Meee. Meeee., (8888) 88, 888888. |
[248] | Meee-Meeeeeee, M.; Meeeee, M.-M.; Meeeee, M., Meee. Meee. Meee, (8888) 88, 8888; Meee. Meeee., (8888) 88, 88888. |
[251] | Mee, M.; Meeeeeeeeeeeeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[252] | Meeeeeee, M.; Meeee, M.; Meeeee, M.; Meeee, M., Meeeeeeeeeee, (8888) 88, 888. |
[253] | Meeeeeee, M.; Meeeeeee, M.; Meee, M.; Mee, M.; Meeeee, M.; Meeeee, M.; Meeeeeee, M., Meeeeeeeeeee, (8888) 88, 8888. |
[254] | Meeeeeee, M.; Meeeeeeee, M.; Meeeeeee, M.; Meeeee, M.-M.; Mäe, M.; Meeeee, M.; Meeeeeeeee, M.; Meee, M.; Meeee, M.; Mäeeee, M.; Meee, M.-M., MM 888 888, (8888); Meee. Meeee., (8888) 888, 888888. |