Modular Assembly of Furotropones and Benzofurotropones, and Study of Their Physicochemical Properties

Abstract

A rapid and straightforward synthesis of a novel series of furo[2,3-d]tropones (or cyclohepta[b]furan-6-ones) has been developed starting from readily and commercially available materials. Directed α-lithiation of furan-3-carboxaldehydes and subsequent reaction with a variety of aldehydes efficiently provide, in one step, access to 3-formyl-2-furylcarbinols, which are otherwise only accessible with difficulty. The 3-formyl-2-furylcarbinols are further elaborated in two steps to the synthesis of furo[2,3-d]tropones in good yields via sequential bismuth(III)chloride-catalyzed furfurylation and an unusual base promoted cyclization strategy. Thus, diverse polysubstituted furotropones and benzofurotropones can be rapidly assembled. This methodology thereby offers a potential approach for the synthesis of several bioactive natural products containing cyclohepta[b]furan core and also for the buildup of complex molecular architectures through higher order cycloaddition reactions of tropones. Further, the new chromophores have been found to possess promising fluorescence properties. Selective fluorogenic sensing behavior of furotropones toward Fe(3+) ions has also been elucidated.

Preparation of Dibenzofurotropones via Pd-Catalyzed Cyclization

“…It appeared that there was a maximum Stokes shift of 86 nm in the ethanol solution. These observations are quite similar to those of furo [2,3-d]tropones, as reported by Ramasastry's group [19].…”

“…Tropones, a class of non-benzenoid aromatic compounds, have been found in numerous natural products, showing distinct biological activities [1][2][3][4][5]. Aryl-annulated tropone derivatives such as benzotropones [6][7][8][9][10][11][12][13][14][15][16][17] and furotropones [18][19][20][21][22][23] are also attractive molecules because their extended conjugations might exhibit intriguing chemical and photophysical properties (Figure 1A). Considering their application potential, the development of synthesizing tropones annulated with three aromatic rings (Figure 1B) has attracted substantial interest in material chemistry [11][12][13][14][15][16][17].…”

Combined Furan C–H Activation and Furyl Ring-Opening by an Iron(II) Complex

“…Furan is an important motif in biologically active molecules and fine chemicals, − and furan plays a key role in cycloadditions (e.g., Diels–Alder reactions) and transition-metal-mediated reactions to produce aromatic feedstocks and compounds useful in natural product and fine chemical synthesis. − Reactions using furan can involve ring opening. For example, furan ring opening and hydrodeoxygenation of bioderived furan compounds to produce linear alkanes has been achieved in high yields and selectivity. , Transition-metal catalysts, such as pentacarbonyl­(η 2 - cis -cyclooctene)­chromium­(0) and Rh 2 (OAc) 4 , have been reported to ring-open furan compounds to produce substituted organic products. − …”

Copper(II)‐Mediated Intermolecular Radical [3+2]‐Annulation of N,N‐Dimethyl Enaminones: Direct Access to 5‐Acyl‐3‐Furancarboxaldehydes

“…While abundant reliable approaches have been established to construct furans, [4] synthetic strategies for the efficient construction of 3‐formylfurans remained limited. Traditionally, 3‐formylfurans could be synthesized from the oxidation of furan‐3‐ylmethanols, [3e,5] or the 3‐formylation of furans (Scheme 1a) [2b,6] . However, these reactions are limited by the pre‐preparation of furan ring through multistep reactions with the harsh reaction conditions and tedious workup procedures.…”