Optically enriched alkyltrimethylsilanes by Haller-Bauer cleavage of optically active, nonenolizable .alpha.-silyl phenyl ketones

Abstract

ChemInform Abstract The chiral menthyl esters (I) are converted to the phenyl ketones (III) by consecutive reductive cleavage, phenylation, and oxidation. The α-silyl ketones (III) are subjected to the Haller-Bauer cleavage reaction, producing the tertiary silanes (IV) with 88 -92% retention of the configuration.

Synthesis of the 1,6,8-trioxadispiro[4.1.5.2]tetradec-11-ene ring system present in the spirolide family of shellfish toxins and its conversion into a 1,6,8-trioxadispiro[4.1.5.2]-tetradec-9-en-12-ol via base-induced rearrangement of an epoxide

“…the C-4 methyl substituent hindering access to the secondary triethylsilyl ether. Alcohols 13 were therefore best prepared by deprotection of bis-silyl ethers 32 using hydrogen chloride in pyridine 19 for 48 h. (2R,3R)-5,5,6-Bis-spiroacetals 12 were then successfully obtained as an equimolar mixture of four diastereomers in 83% yield upon further irradiation with iodobenzene diacetate and iodine.…”

A Radical Version of the Bromo‐ and the Iodocyclization of Bis(homoallylic) Alcohols — The Synthesis of Halogenated Tetrahydrofurans by Stereoselective Alkoxyl Radical Ring Closures

“…7). 5-Methyl-1-phenyl-4-hexen-1-ol (1a), [21] 5-methyl-2-phenyl-4-hexen-1-ol (1b), [25] 2-phenyl-4-hexen-1-ol (1f), [20] 3-phenyl-4-penten-1-ol (1h), [20] 2-bromo-2-chlorodimedone, [34] diethyl 2-bromo-2-methylmalonate, [35] diethyl 2-iodo-2-methylmalonate, [35] 2,2Ј-dithiopyridine-1,1Ј-dioxide, [28] Nhydroxypyridine-2(1H)-thione, [28] (E)-4-phenyl-3-buten-1-ol, [58] and 1-chloro-5-methyl-1-phenyl-4-hexene [21] were prepared according to published procedures. Trapping reagents BrCCl 3 , n-BrC 6 F 13 , Br 2 C 2 Cl 4 , CHI 3 , n-C 4 F 9 I were obtained from commercial suppliers and were used as received.…”

“…[24] Treatment of this chloride with a 2.6-fold excess of 4-(p-chlorophenyl)-N-hydroxythiazole-2(3H)-thione tetraethylammonium salt provided, upon work up of the reaction mixture, 57% of 4-(p-chlorophenyl)-N-(5-methyl-1-phenyl-4-hexen-1-oxy)thiazole-2(3H)-thione (6a, entry 1, Table 1) and 1,2-bis[4-(p-chlorophenyl)-2-thiazyl]disulfane (23%, not shown in Table 1). [23] 2-, and 3-Phenylsubstituted bis(homoallylic) alcohols 1b, [25] 1c, and 1f [26] were esterified with p-toluenesulfonyl chloride in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) to furnish the corresponding tosylates (96% from 1b, 88% from 1c, and 83% from 1f, not shown in Table 1). [20,27] Treatment of these alkylating reagents with 4-(p-chlorophenyl)-Nhydroxythiazole-2(3H)-thione tetraethylammonium salt in anhydrous DMF afforded alkoxyl radical precursors 6b, 6c, and 6f [23] in 45Ϫ53% yield (entries 2, 3, 7, Table 1).…”

(Schiff‐base)vanadium(V) Complex‐Catalyzed Oxidations of Substituted Bis(homoallylic) Alcohols − Stereoselective Synthesis of Functionalized Tetrahydrofurans

“…Conversion of 1-tert-butylsubstituted alkenol 11 under these conditions provided 71% of 5-tert-butyl-2-(1-hydroxy-1-methylethyl)tetrahydrofuran (16) (cis/trans ϭ 91:9) and 4% of diastereomerically pure tetrahydropyran trans-21 ( 1 H NMR spectroscopy). Treatment of 2-phenyl-and 2-isopropyl-substituted substrates 12 and 13 [36] with TBHP and vanadium reagent 4g furnished 2,4-disubstituted tetrahydrofuran 17 (55%, cis/trans ϭ 9:91) and 18 (90%, cis/trans ϭ 19:81) as major products. In addition, trans-2,2-dimethyl-5-phenyltetrahydropyran-3-ol (trans-22) was obtained in 4% yield from the oxidation of alkenol 12, whereas formation of 5-isopropyl-substituted tetrahydropyran 23 from substrate 13 was not observed in our experiments.…”