18326-13-1Relevant articles and documents
Enantioselective, Lewis Base-Catalyzed Sulfenocyclization of Polyenes
Tao, Zhonglin,Robb, Kevin A.,Zhao, Kuo,Denmark, Scott E.
supporting information, p. 3569 - 3573 (2018/03/21)
A sulfenium-ion-initiated, catalytic, enantioselective polyene cyclization is described. Homogeranylarenes and ortho-geranylphenols undergo polycyclization in good yield, diastereoselectivity, and enantioselectivity. The stereodetermining step is the generation of an enantiomerically enriched thiiranium ion from a terminal alkene and a sulfenylating agent in the presence of a chiral Lewis basic catalyst. The use of hexafluoroisopropyl alcohol as the solvent is crucial to obtain good yields. The thioether moiety resulting from the reaction can be subsequently transformed into diverse oxygen and carbon functionality postcyclization. The utility of this method is demonstrated by the enantioselective syntheses of (+)-ferruginol and (+)-hinokiol.
Structure and Synthesis of (+)-Shonanol
Matsumoto, Takashi,Imai, Sachihiko,Kawashima, Hiroyuki,Mitsuki, Masanori
, p. 2099 - 2102 (2007/10/02)
The structure of shonanol was restudied and found to be 12-hydroxyabieta-2,8,11,13-tetraen-1-one (1) by the following synthesis.A Grignard reaction of methyl (+)-12-methoxyabieta-8,11,13-trien-18-oate with phenylmagnesium bromide, followed by treatment with lead tetraacetate and calcium carbonate afforded a mixture of Δ3-, Δ4-, and Δ4(18)-19-nor compounds.This was oxidized with selenium dioxide to give (+)-12-methoxy-19-norabieta-4(18),8,11,13-tetraen-3α-ol.This alcohol was converted to (+)-12-methoxyabieta-5,8,11,13-tetraen-3-one (6) by the known procedure.Reduction of 6 with lithium aluminium hydride, followed by catalytic hydrogenation, yielded (+)-12-methoxyabieta-8,11,13-trien-3β-ol (8) and a small amount of its cis isomer.The compound (8) was then converted to (+)-12-methoxyabieta-1,8,11,13-tetraen-3-one (12) by a series of reactions: oxidation with pyridinium chlorochromate, bromination with pyridinium tribromide, and dehydrobromination with lithium carbonate and lithium bromide.Demethylation of 12 with boron tribromide gave (+)-12-hydroxyabieta-1,8,11,13-tetraen-3-one.Oxidation of 12 with alkaline hydrogen peroxide, followed by treatment with hydrazine hydrate, gave (+)-12-methoxyabieta-2,8,11,13-tetraen-1α-ol; this was oxidized with Jones reagent to give the corresponding 1-oxo compound.The 1-oxo compound was finally demethylated with boron tribromide to yield (+)-1, whose spectra were identical with those of natural shonanol.
Cyclisation Reactions: Part VI - Further Study in Biogenetic-type Cyclisation of Epoxy-Olefins
Nasipuri, Dhanonjoy,Samaddar, Ashis K.,Das, Gautam
, p. 727 - 734 (2007/10/02)
(6E)-9-p-Methoxyphenyl-2,6-dimethylnona-2,6-diene (I) on mono-epoxidation affords mainly 2,3-epoxyolefin (IV) admixed with some 6,7-isomer.IV on cyclisation with boron trifluoride etherate furnishes three ketones: 7-oxo-9-p-methoxyphenyl-2,6-dimethylnon-2-ene (XIII) presumably formed from 6,7-epoxyolefin (XII), cis-3-(2-p-methoxyphenylethyl)-2,2,4-trimethylcyclohexanone (XIV) arising out of 1,4-hydride transfer in an intermediate cyclohexyl cation (XVII), and cis-3-(2-p-methoxyphenylethyl)-2,3,4-trimethylcyclohexanone (XV) resulting from three consecutive 1,2-H, Me shifts in the same intermediate.In addition, 12-methoxypodocarpa-8,11,13-trien-3β-ol (IX) is obtained in 10 percent yield.The mono-epoxide (V) from the corresponding 3-isopropyl-4-methoxyphenyldiene (II) on similar cyclisation affords, among others, hinokiol methyl ether (X) and another crystalline compound characterised by PMR and MS as 12-methoxy-13-isopropyl-A-homo-4a-oxapodocarpa-8,11,13-trien-3β-ol (XXII).The latter is formed by a concerted cyclisation of the di-epoxide (XXI) present in the starting material.Contrary to a previous report from this laboratory, it is now found that trans-podocarpa-8,11,13-trienes (XXV) are more stable than the cis-isomers and are almost the sole products of cyclisation of 2-(2-arylethyl)-1,3,3-trimethylcyclohexyl cations (XXIV) and their analogues under thermodynamically controlled condition.
