Synthetic studies directed toward guianolides: an organoiron route to the 5,7,5 tricyclic ring system

A diastereoselective route to the 5,7,5-tricyclic core of the guianolides is presented. This route relies on Cope rearrangement of a divinylcyclopropane prepared by alkenyl Grignard addition to a (pentadienyl)iron(+1) cation, followed by oxidative decomplexation. An additional key reaction involves oxidative rearrangement of a 3,4-epoxy-1,7-diol to generate a γ-lactone. The relative stereochemistry of this product was established by X-ray crystallography.     

New reaction of formation of the fused tricyclic bispyrroloquinone ring system

A one-pot procedure to difunctionalized fused tricyclic bispyrroloquinone derivatives involving the condensation of N-tosylindoledione and α-ketoamines is described.     

Synthesis of tricyclic analogues of methyllycaconitine using ring closing metathesis to append a B ring to an AE azabicyclic fragment

The synthesis of several ABE tricyclic analogues of the alkaloid methyllycaconitine 1 is reported. The analogues contain two key pharmacophores: a homocholine motif formed from a tertiary N-ethyl amine in a 3-azabicyclo[3.3.1]nonane ring system and a 2-(3-methyl-2,5-dioxopyrrolidin-1-ly)benzoate ester 4. The synthesis of the ABE tricyclic analogues of MLA 1 began with selective allylation at C-3 of 3 to produce allyl beta-keto ester 4. Double Mannich reaction of 4 with ethylamine and formaldehyde produced bicyclic amine 5 The C-9 ketone of bicyclic amine 5 was selectively reduced to form bicyclic alcohols 6 and 7 which were subsequently allylated to form dienes 8 and 9. Ring closing metathesis of dienes 8 and 9 afforded tricyclic ethers 11 and 12, respectively, the C-8 ester of which was reduced to a hydroxymethyl group to form ABE tricyclic analogues 13 and 14. Addition of allylmagnesium bromide to the C-9 ketone of 20 afforded dienes 21 and 22, which underwent ring closing metathesis to form tricyclic esters 23 and 24, respectively. Reduction of the C-8 ethyl ester of 23 and 24 to a hydroxymethyl group afforded diols 25 and 26 respectively. The 2-(3-methyl-2,5-dioxopyrrolin-1-ly)benzoate ester was introduced by conversion of alcohols 13, 14, 25 and 26, to the anthranilate esters 16, 17, 27 and 28 using N-(trifluoroacetyl)anthranilic acid 15 followed by fusion with methylsuccinic anhydride to afford the substituted anthranilates 18, 19, 29 and 30 containing the key 2-(3-methyl-2,5-dioxopyrrolidin-1-ly)benzoate ester pharmacophore.     

Preparation of novel tricyclic ring systems containing the pyridazinone ring

Novel tricyclic ring systems, irmdazo[3,4-d]pyridazino[4,5-b][1,4]thiazines 3 , imidazo[2,1-b]pyridazino[4,5-e][1,3,4]thiadiazines 15 and 18 were prepared by the reaction of 5-amino-4-chloropyridazin-3(2H)-ones 1 and 5(4)-(1-methylhydrazino)-4(5)-chloropyridazin-3(2H)-ones 13 (16) with isothiocyanates 2 and 7 .     

Porphyrins with a novel exocyclic ring system in an oil shale

A C₃₂ and a C₃₁ alkyl porphyrin, each present in Serpiano oil shale as the vanadyl complex, have been -isolated as the demetallated compounds and their structures determined by ¹H NMR spectroscopic analysis of the zinc complexes, using selective decoupling and nuclear Overhauser effects. The occurrence of these chiral optically inactive compounds with a methyl-substituted, six membered exocyclic ring extends the known series of isomeric structural types of sedimentary alkyl porphyrins.     

Synthesis of tricyclic compounds with sulfur and silicon heteroatoms in the central ring

The synthesis of tricyclic derivatives which contain both silicon and sulfur in a central six-, seven- and eight-membered ring are described. Phenothiasilin-5,5-dioxides are prepared by treatment of (o-LiC₆H₄)₂SO₂ with dichlorosilanes. Reduction of the sulfone group is described as well as attempts to introduce aminopropyl substituents at silicon. Thiasilepins are prepared from the Grignard reagent of (o-BrC₆H₄CH₂SC₆H₄Br-o) and reactions of this ring system are described. Reaction of Me₂Si(C₆H₄CH₂Br-o) with Na₂S gave a thiasilocin derivative.     

Mu-28: an open-framework fluorogallophosphate with a three-dimensional 12-membered ring channel system

A new three-dimensional (3-D) microporous fluorogallophosphate, named Mu-28, was obtained by hydrothermal synthesis. It was obtained in the presence of fluoride ions with 1,4-dimethylpiperazine as organic template. This new fluorogallophosphate, with chemical formula [Ga₂₀P₂₀O₈₀(OH)₆F₆(H₂O)₄(C₆H₁₆N₂)₆] 8H₂O, crystallizes in the monoclinic system space group P2₁ with the following unit cell parameters: , , , β=95.10(9)° (Z=1, R₁=0.0435 [I>2σ(I)]). Its structure was determined by single-crystal X-ray diffraction with the help of ³¹P NMR spectroscopy. Mu-28 consists of a complex arrangement of GaO₃(OH,F)(H₂O)₂, GaO₄(OH)F and GaO₄(OH)₂ octahedra, GaO₄F trigonal bipyramids and GaO₃(OH,F) and PO₄ tetrahedra. It displays a 3-D channel system delimited by 12-membered ring openings.     

A convergent synthesis of the tricyclic architecture of the guanacastepenes featuring a selective ring fragmentation

[reaction: see text] This Letter describes a concise, diastereoselective synthesis of the tricyclic carbon framework of the guanacastepene family of natural products. An intermolecular Diels-Alder reaction established a remote stereochemical relationship and facilitated a synthesis of allylic acetate 3, which was subsequently joined with vinylstananne 9 via a Stille coupling. An intramolecular [2 + 2] photocycloaddition then afforded complex cyclobutyl ketone 19, which underwent a stereoelectronically controlled fragmentation to the guanacastepene architecture on treatment with samarium diiodide.