Flavanoid epoxides—XIII

Abstract

2'-Tosyloxychalcon.e epoxide (6a) on reaction with alkali gave flavonol (4a) while similar treatment of 6'-methoxy-2'-tosyloxychalcone•epoxide (6b), both at room temperature and. at the boiling point of the reaction medium, afforded 5-methoxyaurone (Sb). The latter result indicates that an epoxide is not an intermediate in the production of flavanols from 2'-hydroxy-6'-methoxychalcone epoxides on treatment with alkaline hydrogen peroxide (AFO Reaction) at the higher temperature. Epoxide 6a on treatment with boron trifluoride etherate gave a mixture of flavanonol and flavonol while epoxide 6b gave.formyldesoxybenzoin ( 9) under similar conditions.

Elucidation of the Structure of the 2-amino-3,5-Dibromochalcone Epoxides in Solution and Solid State

“…The instability of the 2-hydroxychalcone epoxides under Algar-Flynn-Oyamada reaction conditions is presumably due to the increased acidity of the hydroxyl group that becomes deprotonated under strongly basic conditions to effect nucleophilic attack on the electrophilic epoxide moiety. 2-Hydroxychalcone epoxides substituted at the 6-position of ring-A with a methoxy or methyl group and no hydroxyl group at the ortho or para position of ring-B were found to undergo α-cyclization preferentially to afford aurone derivatives [8]. It is envisaged that the 6-substituent forces the carbonyl group to lie out-of-plane with the aromatic ring and thereby facilitate α-cyclization to afford aurones [9].…”

Semisynthesis of Bioactive Flavonols and Aurones from Naringin

“…一平面上, 从而导致酚羟基距离羰基 α 位较近. 在关环 过程中, 酚负离子优先进攻距离较近的 α 位, 得到五元 环的橙酮类化合物 [16] . 由于空间位阻和热力学稳定关 系, 形成五元环比形成六元环的能量低, 在低温条件下 生成五元环的橙酮化合物占主导地位(Scheme 3).…”

Synthetic Studies Towards the Preparation of 2‐Benzyl‐2‐hydroxybenzofuran‐3(2H)‐one, the Prototype of Naturally Occurring Hydrated Auronols.

“…A mixture of 1 (2 g, 8.9 mmol), Et 2 NH (3.25 g, 44.5 mmol), and dioxane (135 ml) was stirred at 0 ± 58. 13 C-NMR: 73.62 (C(3)); 83.87 (C(2)); 118.13 (C(8)); 118.50 (C(4a)); 122.11 (C(6)); 127.33 (C(5)); 127.53 (C(2'), C(6')); 128.71 (C(3'), C(5')); 129.33 (C(4')); 136.28 (C(1')); 136.94 (C (7) (Z)-2-Benzylidenebenzofuran-3(2H)-one (6). H 2 O 2 soln.…”