Science of Synthesis

Uyanik, M.; Ishihara, K., Science of Synthesis: Catalytic Oxidation in Organic Synthesis, (2017) 1, 666.

Oxidative cyclization of 2-(ω-oxoalkyl)phenols using a chiral ammonium hypoiodite with hydrogen peroxide, tert-butyl hydroperoxide, or cumene hydroperoxide as oxidants proceeds with excellent chemoselectivity and no phenol oxidation products are detected (‌Scheme 37‌).[‌44‌] In sharp contrast, the oxidation of phenols with organoiodine(III) is well known.[‌65‌] The use of chiral binaphthyl-based quaternary ammonium iodide as a catalyst[‌85‌] and an N-phenylimidazol-2-yl group[‌86‌] as an auxiliary to the ketones is effective for inducing high enantioselectivities. The enantioselective oxidative five-membered ring cyclization of β-(2-hydroxyphenyl) ketones ‌76‌ using (R,R)-‌74‌ as the catalyst affords 2-acyl-2,3-dihydrobenzofurans ‌77‌ in excellent yields with high enantioselectivities.[‌44‌] Both aqueous hydrogen peroxide and anhydrous tert-butyl hydroperoxide can be used as an oxidant. Notably, the oxidation of the α-methyl-substituted substrate ‌76‌ (R1 = R2 = R3 = H; R4 = Me) gives the corresponding product ‌77‌ bearing a tetrasubstituted stereogenic center with 96% ee.[‌44‌] However, the enantioselective oxidative six-membered ring cyclization of hydroquinone-derived γ-(2-hydroxyphenyl) ketones ‌78‌ and ‌80‌ directed toward α-tocopherols ‌79‌ and ‌81‌, respectively, does not proceed under identical conditions to that of the five-membered ring cyclization, which uses hydrogen peroxide as an oxidant.[‌87‌] These results suggest that six-membered oxidative cyclization is much slower than five-membered cyclization, and undesired side reactions such as the dearomatization of the phenol moiety become competitive.

Mee eeeeee ee eeeeeee ee eee 8-eeeeeeeeeeeee eeeeeeee ee eeeeeeeeee eeee eeeeeeee-eeeeeeeeeee eeeeeeeeee eeeeee ee eeeeeee eee eee eeeeeeeeeeeeee eeeeeeeee eeeeee—eeeeee eeeeeeee, eeeee eeeeeeee-eeee 8-eeeeeeeeeeeee eeeeeeee eee eeeeee eeeeeeeeeeee. Meeee- eee eeeeeeeeeeeeeeee eeeeeeeee eee-eeeeeeee eeee eeeeeeeeeee ee eeeee-eeeeeeeee eeeeeeeeeeee-eeeeeee γ-(8-eeeeeeeeeeeee) eeeeeee ‌88‌ eeeee eee eeeeeeeeeeeee 8-eeeeeeeeeeeeeeeeeeeeee ‌88‌ eeeeeee e eeeeeeeeee eeeeeeeeeeee ee eeeeee eeeeeeeee eeeeeeeeeeeee eee eee eeeee ee eeeeeeeeeee (α, β, γ, δ) ee eeee ee eee eeeee ee eeeeeeeeeeee (α, β, γ, δ) eeeeeeeeeeeeee eeee eeeeeeeee eeeeeeeeeeeeeeeeeeee.[‌88‌] Meeeeeeeeee, eee eee ee eeeeeeeeeeeeee-eeeeeeeeeee eeeeeeee eeeeee (M,M)-‌88‌ ee e eeeeeeee eee eeeeee eeeeeeeeeeeee ee ee eeeeeee ee eeeeeee ee eeeeee eeee eeeeeeeeeeeeeeeeeeee. Meeee eeeeeeeeeeeee eeeeeeee ee e eeeeeeee ee eeeeeeee eeeeee eee eeee-eeeee eeeeeeeeeeeee eeeeeee eee ee eeee eeeeeeeeee ee eee eeeeeeeeee eeee ee ee eeeeeeee eeeeeeeee eeeeee eeeeeee eee eeeeeeeee eeee ee e eeeeee eeeee eeeeeee. M eeee-eeeeeeeeeee eeeeeeeee eeeeeeeee eeeeee (eeeeeeee eeeeee ee eee eeeeeeee ≤8888) ee eeeeeeee ee eeeeeeeeee eeeeeee eeeeeee eeeeeeeeee eee eeeeeeeee ee eee eeeeeeee ee ee eeeeeeeee eeee eeee ee eeeeeeeee eeeeeeeee. Meee eeeeeeeeeeeeeeee eeeeeeeeee eeeeeeeee eee ee eeeeeee ee eee eeeeeeeee eeeeeeeeeeeeeeeeeee ee δ-eeeeeee eeeeee eeeeeeeeeee.[‌88‌] Mee eeeeeeeeeeeee 8-eeeeeeeeeeeeeeeeeeee eee eeeeeeee ee eeee eeeeeeee eeeee eeee eeee eeeeeeeeeeeeeeeeee.

‌Meeeee 88‌ Meeeee Meeeeeee Meeeeeeeee-Meeeeeeee Meeeeeeee Meeeeeeeeeeeeeeeeee ee β- eee γ-(8-Meeeeeeeeeeee) Meeeeee[‌88‌,‌88‌]

‌Meeeeeeeeee 88‌

e 8.88 eee% ee (M,M)-‌88‌ eee eeee.

‌Meeeeeeeeee 88M‌

e 8.8 eee% ee (M,M)-‌88‌ eee eeee.

‌Meeeeeeeeee 88M‌

M8	M8	M8	Meeeeeeeee	ee (%)	Meeee (%)	Mee
	M	Me	eeeeee eeeeeeeeeeeee, M8MM8, Me8M, ee	88	88	[‌88‌]
M	MMe	Me	e-MeMMM, Me8M, 8 °M	88	88	[‌88‌]

Meeeeeeeeeee Meeeeeeee

(M)-8-(eeee-Meeeeeeeeeeeeeeeeee)-8,8,8,8-eeeeeeeeeee-8-(8-eeeeee-8M-eeeeeeee-8-eeeeeeeeee)-8,8-eeeeeeeeeeee[e]eeeee (‌88‌, M8 = M8 = M8 = Me; M8 = MMMMMM); Meeeeee Meeeeeeee:[‌88‌]

Me e eeeeeee eeeeeee ee 8-[8-(eeee-eeeeeeeeeeeeeeeeeee)-8-eeeeeee-8,8,8-eeeeeeeeeeeeeee]-8-eeeeee-8-(8-eeeeee-8M-eeeeeeee-8-ee)eeeeee-8-eee (‌88‌, M8 = M8 = M8 = Me; M8 = MMMMMM; 88.8 ee, 8.88 eeee, 8.8 eeeee) eee eeeeeeee (M,M)-‌88‌ (8.88 ee, 8.888 eeee, 88 eee%) ee e-MeMMe (8.8 eM) eee eeeee 88 ee% ee M8M8 (88 µM, 8.8 eeee, 8.8 eeeee) ee 88 °M (MMM eeeeeeeeee). Meeee eeeeeeee eee 88 eee, eee eeeeeeeee eeeeeee eee eeeeee eeee eee. ee Me8M8M8 (8 eM). Mee eeeeeee eeeee eee eeeeeeeee eee eeeeeeeee eeee MeMMe (8 ×). Mee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee eeeee eee eeeee (MeMM8). Mee eeeeeee eee eeeeeee eeeee eeeeeee eeeeeeee eee eee eeeeeee eee eeeeeeee ee eeeeeeeeeeeeee (eeeeee eee, eeeeee/MeMMe); eeeee: 88.8 ee (88%); 88% ee.

(M)-8,8,8,8-Meeeeeeeeee-8-(8-eeeeee-8M-eeeeeeee-8-eeeeeeeeee)-8,8-eeeeeee-8M-8-eeeeeeeeee-8-ee 8-Meeeeeeeeeeeeeee (‌88‌, M8 = M8 = Me; M8 = MMe); Meeeeee Meeeeeeee:[‌88‌]

Me e eeeeeee eeeeeee ee 8-eeeeeee-8,8,8-eeeeeeeee-8-[8-eeeeee-8-eee-8-(8-eeeeee-8M-eeeeeeee-8-ee)eeeee]eeeeee 8-eeeeeeeeeeeeeeee (‌88‌, M8 = M8 = Me; M8 = MMe; 8.88 e, 8.8 eeee, 8.8 eeeee), eeeeeeee (M,M)-‌88‌ (88.8 ee, 8.8888 eeee, 8.8 eee%), eee M8MM8 (888 ee, 8.8 eeee, 8.8 eeeee) ee Me8M (888 eM) eee eeeee eeeeee eeeeeeeeeeeee (eeeeeeee ee. 88% eeeeeeee eeeeeeeeeee, 8.88 eM, 8.8 eeee, 8.8 eeeee) ee 88 °M (MMM eeeeeeeeee). Meeee eeeeeeee eee 88 e, eee eeeeeeeee eeeeeee eee eeeeee eeee eee. ee Me8M8M8 (88 eM). Mee eeeeeee eeeee eee eeeeeeeee eee eeeeeeeee eeee MeMMe (8 ×). Mee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee eeeee eee eeeee (MeMM8). Mee eeeeeee eee eeeeeee eeeee eeeeeee eeeeeeee eee eee eeeeeee eee eeeeeeee ee eeeeeeeeeeeeee (eeeeee eee, eeeeee/MeMMe); eeeee: 8.88 e (88%); 88% ee.

References