Pinacol‐Pinacolone Rearrangement of 1, 2‐Di‐(p‐methoxyphenyl)‐ethane‐1, 2‐diol and Bis‐(4‐methoxyphenyl)‐acetaldehyde in Acid Media

Abstract

Die Elcmentaranalysen wurden im mikroanalytischen Laboratorium der ETH Zurich (Leitung : W . Manser) ausgefuhrt. Die NMR.-Spektren wurden in unscrer Instrumentalabteilung (Leitung fur NMR.-Service : Prof. J . F . M . 0 t h ) aufgenommen. Die masscnspektroskopischen Analysen verdanlren wir Herrni PD Dr.Summary. l,Z-Di-(p-methoxyphenyl)-ethanc-l, 2-diol gave in acid media bis-(4-methoxy-pheny1)-acetaldehyde, 4,4'-dimethoxy-deoxybenzoin, and 1, 2-di-(p-methoxypheny1)-ethylenc oxide; their respective yields being influenced by a t least 3 factors: (i) the acid, (ii) its concentration, and (iii) the reaction period.Bis-(4-methoxyplienyl)-acetaldehyde rearranged to the deoxybcnzoin in boiling sulfuric (50 yo) or phosphoric (75%) acids ( w / w ) , and to two isomeric 1,2-diacetoxy-l, 2-di-(p-methoxypheny1)ethanes when it was heated with acetic anhydride.The mechanisms of these reactions are discussed.

Tuning the Selectivity: Study of Solvent‐Free Acid‐Mediated Pinacolic‐Pinacolone Rearrangement under Microwave Irradiation

“…As expected, water decreased the rate of reaction without impact on selectivity. Supported acids were then synthetized by wet impregnation of liquid Brönsted acids on mineral clays at the same concentration ( Table 2, entries [18][19][20][21]. Orthophosphoric acid supported on silica allowed the total conversion of pinacol 1 a with a good selectivity towards the aldehyde 3 a (Table 2, entry 18).…”

“…[12][13][14][15] Its synthetic utility, various theoretical aspects, including mechanistic considerations, have been thoroughly discussed in different reviews. [16][17] Typically, the reaction has been reported using strong Brönsted acids, [18][19][20][21] Lewis acids [22][23][24] as well as solid-supported ones, [25][26][27][28][29][30][31][32] heteropolyacids, [33][34][35] ionic liquids [36] or crystals [37] or aminium salts. [38] Alternative conditions have also been reported such as subcritical water, [39] microwave irradiation [22,29,36,[40][41][42] or solvent-free reaction.…”

Synthetic studies on O-heterocycles via cycloadditions. Part 1. Photochemical (electron transfer sensitised) C-C cleavage of diaryloxiranes

“…At this stage we had easy access to the lactone (19), epimeric at C-2 and C-4 with the target (14) and lacking the aryl oxygenation, and the tetrahydrofuran (25) with the stereochemistry of veraguensin (15), but again lacking the appropriate aromatic substitutents. Since p-oxygenated aryl substituents a to tetahydrofuran oxygens are known, in natural lignans, to epimerise readily in dilute acid,' ' we projected that the 3,4-methylenedioxy analogue of (16) would epimerise under mild conditions to the more stable stereochemistry of the target (14). We thus set out to investigate the crucial question of the effects of aryl oxygen substitution on the ring-opening reactions of stilbene oxides.…”

“…This furan or its analogues might perhaps be of use, e.g. the bis(methy1enedioxy) analogue would serve as a base to prepare the lactone (14) following the reaction scheme employed by Lavie and co-workers" to prepare the lactone (17) from dimethyl 2,5-diphenylfuran-3,4dicarboxylate. However such approaches would be limited by the lack of regioselectivity which would certainly be seen in the chemistry of oxiranes substituted by two aryls carrying different oxygenation patterns.…”