The readily available o-acetylenic Baylis-Hillman adduct acetates 1a-d, whose preparation has been previously described [23], provided a convenient starting point for the synthesis of this ring system, as shown in Scheme . Treatment of Baylis-Hillman acetates 1a-d with sodium nitrite in N,N-dimethylformamide at room temperature for 1.5-10 hours afforded o-acetylenic 2-nitromethylcinnamic acid methyl esters 2a-d in 20-70% yields [17b]. A better

Treatment of propiolic acid esters or N,N-dimethylpropynamide and various 2-biphenylcarboxaldehydes with tetrabutylammonium iodide/zirconium(IV) chloride, titanium(IV) chloride/ dimethyl sulfide, or titanium(IV) bromide/dimethyl sulfide or treatment of methyl acrylate and 2-biphenylcarboxaldehydes with 1,4-diazabicyclo[2.2.2]octane (DABCO) and triethanolamine induce an aldol-type reaction to furnish b-halo-a-(hydroxymethyl)acrylates or a-(hydroxymethyl)acrylates, respectively. These can be used for the preparation of 2-(9H-fluoren-9-yl)acrylic acid derivatives by intramolecular Friedel-Crafts reaction with sulfuric acid in tetrachloromethane.The Morita-Baylis-Hillman (MBH) chemistry has become one of the important and attractive sources for chemical transformations in synthetic organic chemistry and is of current interest. 1 The Friedel-Crafts reaction is one of the most fundamental carbon-carbon bond forming reaction in organic synthesis. 2 Recently, Basavaiah and Kim independently reported the syntheses of a variety of compounds from MBH adducts with the Friedel-Crafts reaction as the key step. These include syntheses of 2-benzylcinnamates, 3 indenes, 4 2-arylideneindan-1-ones, 5 indenoquinolines, 6 and 2-quinolones. 7 During continued efforts to develop MBH chemistry, 8 we envisioned that we could synthesize the fluorene derivatives 4 from MBH adducts of 2-biphenylcarboxaldehydes 2 by an intramolecular Friedel-Crafts reaction as shown in Scheme 1.Fluorene is the core structure of naturally occurring potent molecules such as the MTP inhibitor, 9 interferon inducers 10 and antitumor compounds. 11 Fluorenes in polymer structures have also attracted much attention as molecular devices for blue-light-emitting materials. 12 The 9-fluorenylmethoxycarbonyl (Fmoc) group has tremendous popularity as a protecting group for amines in the synthesis of peptides and related compounds. 13 Although there are numerous reports on the synthesis of fluorenes 14 including the Friedel-Crafts method, 15 there has not been a report on the Friedel-Crafts intramolecular cyclization of MBH adducts of 2-biphenylcarboxaldehydes to give fluorenes.The required b-iodo-MBH adducts 2a-e were prepared by the reaction of alkyl propiolates or N,N-dimethylpropynamide with tetrabutylammonium iodide, followed by an aldol process with aldehydes 1a-c in the presence of zirconium(IV) chloride in 55-81% yields, originally reported by Taniguchi 16 and Lu. 17,18 The b-chloro-MBH adduct 2f (52%) and b-bromo-MBH adduct 2g (22%) were obtained by the reaction of methyl propiolate with 2-biphenylcarboxaldehyde (1a) in the presence of titanium(IV) chloride/dimethyl sulfide or titanium(IV) bromide/dimethyl sulfide, respectively, according to the Kataoka procedure. 19 In the 1 H NMR spectra, the characteristic chemical shift of the alkenic protons of 2a-g were found at d = 6.43-7.18 as a doublet due to allylic coupling (J = 1.2-1.5 Hz). In all cases, the stereoselectivity was found to be 100% Z-selectivity, as determined by 1 H NMR analysis in comparison with li...

Synthesis of 2-(9-Fluorenyl)acrylic Acid Derivatives via Intramolecular Friedel-Crafts Reaction of Morita-Baylis-Hillman Adducts of 2-Biphenylcarboxaldehydes. -The method is presented with a view to the importance of fluorene building blocks in syntheses of bioactive molecules and in material sciences. -(LIM, H. N.; JI, S.-H.; LEE*, K.-J.; Synthesis 2007, 16, 2454-2460; Dep. Chem. Eng., Hanyang Univ., Seoul 133-791, S. Korea; Eng.) -Nuesgen 51-130