A novel photochemical ring contraction of 11a-methylpterocarpans
TL;DR: In this paper, a novel photochemical ring contraction of 6H-(benzofuro)(3,2-c)(1)11a,6a-dihydro-11a-methylbenzopyrans, 1 or shortly, 11a,methylpterocarpans, 2 is reported.
Abstract: A novel photochemical ring contraction of 6H-(benzofuro)(3,2-c)(1)11a,6a-dihydro-11a-methylbenzopyrans, 1 or shortly, 11a-methylpterocarpans to the respective 4b,9b-dihydro-4b,9b-dimethylbenzofuro(3,2-b)benzofurans 2 is reported. This transformation of 1 → 2 is envisaged to proceed through a mechanism involving the intermediacy of 6 . An unusual acceleration of this photochemical rearrangement by bases has been observed.
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TL;DR: The development of a unique cationic polyene cyclization for the total synthesis of the tetracyclic meroterpenoid (-)-cyclosmenospongine is reported, proceeding in a highly efficient manner to give exclusively the trans-decalin framework.
Abstract: We report a full account on the development of a unique cationic polyene cyclization for the total synthesis of the tetracyclic meroterpenoid (-)-cyclosmenospongine. A highly convergent three-component coupling strategy enabled rapid access to individual cyclization precursors that were tested for their reactivity. The successful transformation generates three rings and sets four consecutive stereocenters in a single operation proceeding in a highly efficient manner to give exclusively the trans-decalin framework. In addition, we found that the enol ether geometry and the relative configuration of C3 and C8 are crucial for the success of the polyene cyclization.
22 citations
Patent•
14 Mar 1996
TL;DR: In this paper, the structural formula of polyaromatic heterocyclic compounds has been studied for the treatment of a wide variety of disease states, whether human or veterinary, for example dermatological, rheumatic, respiratory, cardiovascular and ophthalmological disorders.
Abstract: Novel pharmaceutically/cosmetically-active polyaromatic heterocyclic compounds have the structural formula (I): ##STR1## in which Z is a divalent radical selected from among --O--, --S-- or --Nr'-- and Ar is either a radical having the following structural formula (II): ##STR2## or a radical having the following structural formula (III): ##STR3## and are useful for the treatment of a wide variety of disease states, whether human or veterinary, for example dermatological, rheumatic, respiratory, cardiovascular and ophthalmological disorders, as well as for the treatment of mammalian skin and hair conditions/disorders.
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TL;DR: In this article, 2-(1′-Arylallyl)-phenols (9, 10, 11, 12, 13, 14, 15, 16) were transformed on heating in N, N-diethylaniline at 225° into trans-2-aryl-3-methyl-coumarans (26, 29, 32, 34, 36, 38, 40, 42) in excellent yields.
Abstract: 2-(1′-Arylallyl)-phenols (9, 10, 11, 12, 13, 14, 15, 16) are transformed on heating in N, N-diethylaniline at 225° into trans-2-aryl-3-methyl-coumarans (26, 29, 32, 34, 36, 38, 40, 42) in excellent yields. The corresponding cis-coumarans are minor products. Similar thermal behaviour is shown by 2-(1′-vinylallyl)-phenols (7, 8) which are thermally converted into trans-3-methyl-2-vinyl-coumarans (24, 19) and 5-methyl-2,5-dihydro-(1-benzoxepins) (25, 18). The latter compounds are thermally unstable and rearrange to give approximatively 3:1 mixtures of trans- and cis-3-methyl-2-vinyl-coumarans (24, 19). Reaction mechanisms for these new thermal rearrangements are discussed in schemes 2, 3 and 4.
The 2-(1′-arylallyl)-phenols 9, 12 and 14 yield under acidic conditions (HBr/HOAc) the expected 3-aryl-2-methyl-coumarans 28, 35, 39 along with 2-aryl-3-methyl-coumarans 26, 34, 38 and 2-aryl-2-methyl-coumarans 44, 45, 46. The intervention of phenonium ions is discussed for these reactions (cf. scheme 5).
When the 2-(1′-arylallyl)-phenols 12 and 14 were irradiated in benzene solution with a mercury high pressure lamp, the main products obtained were 3-aryl-2-methyl-coumarans 35 and 39 which were formed rapidly. 2-Aryl-3-methyl-coumarans yield also 3-aryl-2-methyl-coumarans, when irradiated in benzene solution.
38 citations
TL;DR: In this article, a successful Claisen rearrangement of a number of 1,4-diaryloxy-2-butynes is reported, which offers a facile synthetic route to tetracyclic derivatives resembling the naturally occurring pterocarpans.
Abstract: Successful Claisen rearrangement of a number of 1,4-diaryloxy-2-butynes is reported. The products of such a rearrangement are the benzofuro[3,2-c]benzopyrans. This novel rearrangement offers a facile synthetic route to tetracyclic derivatives resembling the naturally occurring pterocarpans.
29 citations
27 citations
27 citations
TL;DR: In this article, two conceivable mechanistic pathways in the conversion of 1,4-diaryloxy-2butynes to benzofurobenzopyrans, one is eliminated and the other validated.
Abstract: Of two conceivable mechanistic pathways in the conversion of 1,4-diaryloxy-2-butynes to benzofurobenzopyrans, one is eliminated and the other validated. Whereas 2-methyl-3-phenoxymethylbenzofuran is resistant to Claisen rearrangement, 4-phenoxymethyl-Δ3-chromene undergoes such a rearrangement with concomitant ring closure to the benzofurobenzopyran (VIII). The related system viz. 4-phenoxymethylcoumarin showed no propensity for similar rearrangement.
23 citations