Tin(II) chloride dihydrate: A mild and efficient reagent for cleaving acetals.

Preparation of Novel Polycyclic Heterocycles Using a Tin(II) Chloride Dihydrate-Mediated Deacetalisation-Bicyclisation Sequence

“…L-Cysteine dimethyl ester dihydrochloride (27; 128 mg, 0.37 mmol) and 3- [1,3]dioxolan-2-ylpropionic acid (15a; 100 mg, 0.68 mmol) were converted into amide 28 according to the procedure used for amide 14a (see above). The unpurified amide 28 was then treated with SnCl 2 •2H 2 O (306 mg, 1.36 mmol) for 72 h following the procedure used in methods A and B above.…”

“…Yield: 82 mg (59% over two steps); clear colourless oil. Oxohexahydropyrrolo[2,1-b Methyl-3,3a,4,9-tetrahydro-2H-pyrrolo[2,1-b]quinazoin-1one (32) Prepared from 2-methylaminobenzylamine (30; 60 mg, 0.43 mmol) 22 and 3- [1,3]dioxolan-2-ylpropionic acid (15a; 58 mg, 0.39 mmol) according to the procedure described for the preparation of compound 13a. The crude amide was stirred with SnCl 2 •2H 2 O (175 mg, 0.78 mmol) for 18 h and the crude product was purified by preparative TLC (EtOAc-PE, 1:1) to yield the title compound 32.…”

“…Tin(II) chloride is widely used as a reducing agent and as a Lewis acid catalyst 2 and, as its dihydrate, has been employed as a mild reagent for the deprotection of acetals. 3 This research was inspired by recent natural product studies in our group which featured the use of SnCl 2 •2H 2 Omediated deprotection-cyclisation processes. As illustrated in Scheme 1, treatment of acetal 1 with SnCl 2 •2H 2 O gave the racemic [6,6,6,6]-tetracyclic core 2 of the HIV-1 integrase inhibitors integrastatins A and B via a presumed sequence of acetal deprotection, debenzylation, hemi-acetal formation, and alkene etherification.…”

Metal halide hydrates as lewis acid catalysts for the conjugated friedel-crafts reactions of indoles and activated olefins

“…37 The Lewis acidity of SnCl 2 ·2H 2 O has been reported by others in different reactions types. [38][39][40] Although the hydrogen Brønsted acid catalysis has been suggested by Spencer as the main process when a metal halide is used as a Lewis catalyst in aqueous (or protic alcoholic) solvents, 41 other authors postulated the water-tolerance of many metal halides. Kobayashi suggests that the certain metal halides are able to complex with the electrophile before the hydrolysis occurs.…”

Stereoselective Syntheses of the Octahydropyrano[2,3‐b]pyridine DE Core of 'Upenamide via a Stannous Chloride‐Induced Deacetalisation–Cyclisation Procedure

“…Finally, the reactivity of dioxolane 20 with stannous chloride dihydrate was studied. [7] We were delighted to observe that compound 20 was converted into the required octahydropyrano [2,3-b]pyridine 21 in 65 % yield, and the aza-annulation was stereoselective producing a single diastereoisomer of the DE hemiaminal ring system. The cis ring junction was determined on the basis of the small coupling constant between protons 4a-H and 8a-H and the chemical shift of the hemiaminal proton 8a-H (δ Ͼ 4.0 ppm).…”