Synthetic approaches toward spiro[2,3-dihydro-4H-1-benzopyran-4,1'-cyclohexan]-2-one derivatives via radical reactions: total synthesis of (.+-.)-lycoramine

Abstract

Syntheses of spiro[2,3-dihydro-4H-l-benzopyran-4,l'-cyclohexan]-2-one derivatives by reaction sequences including a radical reaction and a total synthesis of (±)-lycoramine (2) are described. Radical reactions (BuaSnH, AIBN) of 1-[(l'-cyclohexenylmethyl)oxy] -2-halobenzenes 23b-d in boiling benzene gave the corresponding spiro[2,3-dihydrobenzofuran-3,l'-cyclohexanes] 26a,b in good yields, whereas the reaction of l-(l'-cyclohexenylethoxy)-2-bromobenzene (25) under similar conditions afforded a mixture of spiro[2,3-dihydro-4H-l-benzopyran-4,l,-cyclohexane] 27 and benzoxepin 28. Furthermore, the radical reaction of ethyl 2-[(2'-bromoaryl)oxy] -1-cyclohexenylacetate 37a produced ethyl 2-spiro[2,3-dihydrobenzofuran-3,l'-cyclohexane]carboxylate 38 in good yield. Compound 38 was converted to spiro[2,3-dihydro-4ff-l-benzopyran-4,l'-cyclohexane]-2,4'-dione 40 by treatment with Sml2 and then with 3 N HC1. Spiro[2,3-dihydro-4H-l-benzopyran-4,l'-cyclohexane]-2,4'-dione 40 was transformed to (±)-lycoramine (2) in four steps and 43% overall yield.

Stereoselective synthesis of a chiral ferrosalen ligand using an aromatization strategy

“…However, we found that this double bond installation was difficult to achieve. A simple method would be heating 7 with benzeneseleninic acid anhydride in toluene [9]. Under these conditions, we were able to synthesize a compound resulting from nucleophilic substitution of the anhydride with the enol of 7.…”

“…This ligand has unique structural features that are expected to be beneficial for improving enantioselectivities of some catalytic reactions. The key benzoferrocenyl building block (9) for the preparation of the ligand was synthesized stereoselectively. The aromatization of enantiopure 7 to benzoferrocene derivative 9 represents an unprecedented strategy for the synthesis of chiral ferrocenyl ligands.…”

Stereoselective synthesis of carbohydrate-based fused bicyclic delta-lactones

“…Several authors reported failure in attempting 5-and 6-exo-trig radical ring closure of ester derivatives due to the geometric constraints associated with the preferred s-Z conformation of the ester function. [14][15][16][17][18][19][20] Thus, the successful Scheme. Reagents and conditions: i) I 2 , Ph 3 P, imidazole, toluene, reflux [70% (7) and 63% (8)]; ii) cinnamic acid or crotonic acid, DCC, DMAP, CH 2 Cl 2 , rt (56-79%).…”

Spirobisnaphthalenes effectively inhibit carbonic anhydrase

“…However, it is assumed that a fungus living in this plant 16 produced this compound. Meanwhile, a large number of such spiro compounds were isolated mostly from endophytic fungi and named diepoxines 1 , Sch plus number 8,17,18 , CJ-plus number 11 , cladosporins [19][20][21] , palmarumycins 3,[22][23][24] , sphaerolones 25 , decaspirones 4,17 and deoxypreussomerin 26 . The interesting structures, various biological activities and potential applications in agriculture, medicine and the food industry attracted the attention of many research groups with respect to the synthesis of spirobisnaphthalenes.…”