Studies on the intramolecular oxa-Pictet–Spengler rearrangement of 5-aryl-1,3-dioxolanes to 4-hydroxy-isochromans

An alternative and convenient synthesis of oct-7-enal, a naturally-occurring aldehyde isolated from the Japanese thistle Cirsium dipsacolepis

“…As shown in Scheme 2, this comprised the selective monoprotection of one of the hydroxyl groups of the starting material as tert-butyl dimethylsilyl (TBS) ether employing TBSCl and NaH in dry THF, which furnished 60% of compound 10, a yield that was similar to that achieved when TBSCl and imidazole in anhydrous DMF were used. 18 In turn, alcohol 10 was transformed into the related sulfonic ester 11 (86% yield) with tosyl chloride and triethylamine, under conventional conditions, setting the stage for chain elongation. There are scattered precedents of the direct displacement of tosylates by the allyl Grignard; 19 however, it was considered convenient to employ copper (I) iodide assistance, a more established alternative.…”

Microwave‐accelerated Synthesis of Some (±)‐1‐Aryl‐5‐chloroisochromans

“…8 The reaction time varies from 1-day to several days and despite this in some cases the reaction is not complete. 17,18 In the present study, a variety of aromatic aldehydes were condensed with 2-(2-chlorophenyl)ethanol, a non-activated substrate, in the presence of a catalytic amount of a very mild acid catalyst, p-toluenesulfonic acid by microwave irradiation (Scheme 1). Commercial (2-chlorophenyl)-acetic acid was reduced using sodium boron hydride in THF/methanol to afford 2-(2-chlorophenyl)ethanol.…”

“…Typically, aqueous HCl, zinc chloride HCl gas, p-toluenesulfonic acid, titanium tetrachloride or stannic chloride have been used as FriedelCrafts catalysts along with high reaction temperatures. 17 The activated substrates such as 2-(3,4-dihydroxyphenyl)ethanol undergo the oxa-Pictet-Spengler reaction under mild conditions. 9,17,18 However, the reaction time required to obtain the satisfactory yields varied from 1 day for aldehydes to 2 days to ca.…”

Synthesis, Characterization, Anti-Inflammatory and in Vitro Antibacterial Activity of Some (±)-1-Aryl-7,8-Dichloroisochromans

“…Synthesis of title compounds was carried out by oxa-Pictet-Spengler reaction, a variation of the Pictet-Spengler reaction in which a phenethyl alcohol reacts with a carbonyl compound to give a 1-substitued isochroman derivative. Typically, aqueous HCl, zinc chloride-HCl gas, p-toluenesulfonic acid, titanium tetrachloride or stannic chloride have been used as Friedel-Crafts catalysts alongwith high reaction temperatures [17]. The activated substrates such as 2-(3,4-dihydroxy)phenylethanol undergo the oxa-Pictet-Spengler reaction under mild conditions [18].…”