The Paternò-Büchi Reaction of 2-Furylmethanols

D’Auria, Maurizio; Racioppi, Rocco; Romaniello, Gianfranco

doi:10.1002/1099-0690(200010)2000:19<3265::aid-ejoc3265>3.0.co;2-6

Cited by 50 publications

(10 citation statements)

References 27 publications

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“…This group proposed that hydrogen-bond interactions in the exciplex played an important role in controlling the selectivity. DAuria and coworkers also observed a site-selective and diastereoselective formation of oxetanes in the PB reaction of 2-furylmethanol derivatives (Scheme 7.27) [45]. However, hydroxy-directed diastereoselectivity was not generalized to face-selectivity in the PB reaction of hydroxy-substituted dihydrofuran and furan derivatives (Scheme 7.28) [46].…”

Section: Stereoselective Syntheses Of Oxetanesmentioning

confidence: 99%

Formation of a Four‐Membered Ring: Oxetanes

Abe

2009

Handbook of Synthetic Photochemistry

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Oxetanes, four-membered cyclic ethers, have a ring strain energy (SE) of approximately 110 kJ mol À1 [1] and polar properties of the CO bonds (Figure 7.1). Thus, similar to the synthetic utility of oxiranes (epoxides, SE ¼ 114 kJ mol À1 ), the ringopening reaction of oxetanes, accompanying bond-formation reactions, would be very useful for synthetic purposes [2]. Since the oxetane ring is an important structural component of biologically active compounds, such as merrilactone A [3], thromboxane A2 [4], oxetanocin [5], oxetin [6], taxane alkaloids [7], and laureacetal-B [8], efficient and selective methods to synthesize the strained structure are currently active areas of research. Moreover, oxetane-ring-containing compounds are important industrial curing agents [9]. As a consequence, there are today over 2900 patents which include the term oxetane as a key word.All of these findings clearly indicate that the demand for synthetic oxetanes is high. There are basically three methods for preparing oxetanes:1. The intramolecular nucleophilic substitution reaction. 2. The ring-expansion reaction of epoxides. 3. The thermal and photochemical [2 þ 2] cycloaddition reaction of alkenes with carbonyls.The intramolecular nucleophilic substitution reaction -for example, the Williamson-type reaction -represents one of the important methods for preparing oxetane ring structures, and have been widely applied to the synthesis of oxetanes (Scheme 7.1) [10]. Unfortunately, side reactions -which include fragmentation from the intermediary alkoxide anion or elimination from the intermediary carbocation -often decrease the chemical yields of oxetane formation.The ring-expansion reaction of epoxides was first reported by Okuma and coworkers, to produce less-substituted oxetanes (Scheme 7.2) [11]. The nucleophilic attack by dimethyloxosulfonium methylide is proposed to react with the lessHandbook of Synthetic Photochemistry. Edited

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Section: Stereoselective Syntheses Of Oxetanesmentioning

confidence: 99%

Formation of a Four‐Membered Ring: Oxetanes

Abe

2009

Handbook of Synthetic Photochemistry

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“…13 Recently we reported that the reaction between aromatic aldehydes and ketones with 2-furylmethanols give the corresponding adducts in good yields with high regio-, stereo-, and enantioselectivity. 14 We observed that the reaction occurred on the most hindered side of the molecule. This behavior was explained assuming the presence of an electron transfer process (in which the hydroxyl group plays an important role) followed by radical coupling between furyl carbon in α position and the oxygen on the carbonyl group.…”

Section: Methodsmentioning

confidence: 94%

“…Thus, a clear change in the regioselectivity going from 4,4'-dichlorobenzophenone (attack on positions 2,3) to 4,4'-dimethoxybenzophenone (attack on positions 4,5) can be seen, benzophenone showing an intermediate behavior. In our previous work 14 we formulated the hypothesis that the photochemical reaction of 2-furylmethanols with aromatic ketones involves a single electron transfer from the furan derivatives to the ketone followed by radical coupling with the formation of zwitterionic species. In contrast with current opinions in this field, 1 we thought that the most probable structures for these zwitteronic species would be those represented in the Figure. Our point of view can be supported by results of theoretical calculations showing that stability of intermediates explains the regiochemical behavior of the reaction.…”

Section: Methodsmentioning

confidence: 99%

Paterno-Büchi reaction on 5-methyl-2-furylmethanol derivatives

D’Auria¹,

Racioppi²

2000

Arkivoc

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A photochemical reaction of 5-methyl-2-furyl-phenylmethanol (4) with benzophenone gave two 2+2 adducts 5 and 6 in 1:1 ratio. The reactions of 4 with 4,4'-dimethoxybenzophenone, benzaldehyde or 4-methoxybenzaldehyde formed adducts 7, 10 or 11 respectively on the side of furan bearing the methyl group while with 4,4'-dichlorobenzophenone gave 8 on the other side of the molecule. Regiochemistry of the reaction can be explained assuming a single electron transfer process followed by radical coupling of the reagents. The different stability of intermediates explains the observed regioselectivity.

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“…While the reaction of 2-furylmethanol with benzophenone showed low regioselectivity, the presence of larger substituents on the carbon bearing the alcoholic function allows a high regioselectivity (Scheme 7) [37]. Furthermore, when 2-furylethanol (20) was used as substrate, a 1 : 1 mixture of stereoisomers was obtained, while, when 1-(2-furyl)-benzylic alcohol (21) was the substrate, only one diastereoisomer was obtained.…”

Section: Photoaddition Of Carbonyl Compounds To Chiral Furansmentioning

confidence: 99%

“…The reaction of 2-furylphenylmethanol gave complete diastereoisomeric control when it reacted with benzophenone [37]. The conformers of this substrate are reported in Figure 16.…”

Section: Photoaddition Of Carbonyl Compounds To Chiral Furansmentioning

confidence: 99%

Regio- and stereoselectivity in the Paternò–Büchi reaction on furan derivatives

D’Auria

Emanuele

Racioppi

2004

Journal of Photochemistry and Photobiology A: Chemistry

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The photochemical coupling reaction between 2,3-dihydrofuran and benzaldehyde was studied by using DFT/B3LYP/6 − 31G + (d, p) method. The regiocontrol of the attack of the benzaldehyde on the double bond is related to the different stabilities of the biradical intermediates. The endo stereoselectivity of the reaction depends on the superposition between HSOMO and LSOMO in the biradical intermediate. In the photochemical reaction between furan and benzaldehyde also the regiocontrol depends on the relative stability of the possible biradical intermediates. The exo stereoselectivity of the coupling reaction depends on the superposition between the HSOMO and LSOMO of the biradical intermediate. The reaction of chiral phenylglyoxylates with furan gave the corresponding adducts with de = 15-95%. The stereocontrol can be explained considering the energy gap between the biradical intermediates in the coupling reaction. When the reaction was performed in the presence of zeolite, the diastereoisomeric excess increased. The reaction of benzoin and 2-phenylpropiophenone with furan gave the cycloadduct with high diastereocontrol. All the products were obtained with de > 98%. The Paterrnò-Büchi reaction between 2-furylmethanols with aromatic carbonyl compounds also showed high regio-and stereocontrol. On the contrary, when 5-methyl derivatives were used, a lack of regiocontrol was observed. Furthermore, with aliphatic carbonyl compounds, no diastereoselectivity was observed. These results were explained assuming the attack of the excited carbonyl compound on the same side as the hydroxyl group, through the formation of a hydrogen bond or of a complex. This type of attack gave the biradical intermediate in preferential conformations. The relative energies of these conformers account for the observed diastereoselectivity.

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The Paternò-Büchi Reaction of 2-Furylmethanols

Cited by 50 publications

References 27 publications

Formation of a Four‐Membered Ring: Oxetanes

Formation of a Four‐Membered Ring: Oxetanes

Paterno-Büchi reaction on 5-methyl-2-furylmethanol derivatives

Regio- and stereoselectivity in the Paternò–Büchi reaction on furan derivatives

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