“…In the presence of oxygen, UV irradiation of β-aminopropiophenones yielded the products resulting from ring-opening reactions of the corresponding 2-aminocyclopropanols. [82][83][84] R,β-Unsaturated ketones and β-substituted aromatic 1,3-diketones were utilized in photochemical cyclopropanol formation by C 1 -C 3 bond closure. [86][87][88] UV irradiation of dibenzoyl ketone 47 in the presence of triethylamine led to the formation of trans-1,2cyclopropanediol 48 in good yield.…”
Section: Aldehydes and Ketonesmentioning
confidence: 99%
“…Intramolecular hydrogen abstraction in photoexcited β- N , N -dialkylaminopropiophenones leads to hydrogen transfer from the β-carbon to the carbonyl oxygen, resulting in the formation of hydroxy biradicals that can undergo cyclization to form 2-dialkylaminocyclopropanols. − Photocyclization of 45 proceeded regioselectively, involving the β-aminomethylene hydrogen, and resulted in stereoselective formation of 2-benzyl-substituted cyclopropanol 46 in good yield (Scheme ). In the presence of oxygen, UV irradiation of β-aminopropiophenones yielded the products resulting from ring-opening reactions of the corresponding 2-aminocyclopropanols. − 20 …”
“…In the presence of oxygen, UV irradiation of β-aminopropiophenones yielded the products resulting from ring-opening reactions of the corresponding 2-aminocyclopropanols. [82][83][84] R,β-Unsaturated ketones and β-substituted aromatic 1,3-diketones were utilized in photochemical cyclopropanol formation by C 1 -C 3 bond closure. [86][87][88] UV irradiation of dibenzoyl ketone 47 in the presence of triethylamine led to the formation of trans-1,2cyclopropanediol 48 in good yield.…”
Section: Aldehydes and Ketonesmentioning
confidence: 99%
“…Intramolecular hydrogen abstraction in photoexcited β- N , N -dialkylaminopropiophenones leads to hydrogen transfer from the β-carbon to the carbonyl oxygen, resulting in the formation of hydroxy biradicals that can undergo cyclization to form 2-dialkylaminocyclopropanols. − Photocyclization of 45 proceeded regioselectively, involving the β-aminomethylene hydrogen, and resulted in stereoselective formation of 2-benzyl-substituted cyclopropanol 46 in good yield (Scheme ). In the presence of oxygen, UV irradiation of β-aminopropiophenones yielded the products resulting from ring-opening reactions of the corresponding 2-aminocyclopropanols. − 20 …”
“…79 Recently, a-aminoenone 24 was synthesised by photooxidation of cyclopropanol 25. 80 Photolysis was carried out in the presence of photosensitising agents, viz., 9,10-dicyanoanthracene or triphenylpyrylium tetrafluoroborate, for 0.5 ± 5.2 min. It was noted that the enone 24 decomposed when the reaction time was increased.…”
“…4 In virtue of the wide application of a-ketoenamines in organic chemistry, there is still a need to develop facile and practical synthetic methods for their preparation although some methods for the synthesis of this useful class of compounds have been well documented in literature. These methods can be mainly exemplified as follows: (1) the Claisen-Schmidt condensation reaction; 5 (2) the photooxidation of 2-morpholino cyclopropanols; 6 (3) the elimination of molecular nitrogen from a-azidoketones; 7 (4) the ring opening of trans -1,3-dibenzoyl-2-phenylaziridine in the presence of a base; 8 (5) the aminohalogenation reaction of a,b-unsaturated ketones followed by treatment with specific bases. 2 Herein we disclose a new one-pot, two-step synthetic strategy for the preparation of a-ketoenamines through the reactions of a-bromoketones or a-bromoesters 1 with hydroxamates 2, namely, (1) initial displacement of bromide by hydroxamate anion to give the intermediate 3 and (2) base-induced elimination of benzyl alcohol with the subsequent generation of the a,b-double bond.…”
a,b-Dehydroamino acid derivatives were synthesized in good yields from a-bromoketones or a-bromoesters and hydroxamates via a sequential procedure involving displacement of bromide by hydroxamate anion, followed by a base-induced eliminationisomerization reaction.Functionalized enamines have long served as useful building blocks in the synthesis of a variety of different structures which possess biological and medicinal importance. 1 As members of this family, a-ketoenamines (also referred to as a,b-dehydroamino acid derivatives 2 ) occur as frequent subunits in natural products and biologically active compounds and thus play important roles in organic synthesis. 3 They are useful synthons not only in electrophilic and nucleophilic chemistry, but also in photochemistry and electrocyclic reactions, especially for the synthesis of heterocyclic compounds. 4In virtue of the wide application of a-ketoenamines in organic chemistry, there is still a need to develop facile and practical synthetic methods for their preparation although some methods for the synthesis of this useful class of compounds have been well documented in literature. These methods can be mainly exemplified as follows: (1) the Claisen-Schmidt condensation reaction; 5 (2) the photooxidation of 2-morpholino cyclopropanols; 6 (3) the elimination of molecular nitrogen from a-azidoketones; 7 (4) the ring opening of trans-1,3-dibenzoyl-2-phenylaziridine in the presence of a base; 8 (5) the aminohalogenation reaction of a,b-unsaturated ketones followed by treatment with specific bases. 2Herein we disclose a new one-pot, two-step synthetic strategy for the preparation of a-ketoenamines through the reactions of a-bromoketones or a-bromoesters 1 with hydroxamates 2, namely, (1) initial displacement of bromide by hydroxamate anion to give the intermediate 3 and (2) base-induced elimination of benzyl alcohol with the subsequent generation of the a,b-double bond. The two steps were then combined into an efficient standard procedure.The required starting materials 1 and 2 for this approach were conveniently prepared from commercial materials in high yields according to a reported process. 9 Initially, we started research with the model reaction starting from 1a and 2a (Table 1). The conversion was explored by investigating the use of different bases (KOt-Bu, NaH, DBU, Et 3 N, K 2 CO 3 , and Cs 2 CO 3 ) and different solvent systems (DMF, MeCN, THF, CH 2 Cl 2 , and PhMe).In these solvent studies, we found that polar aprotic solvents benefited not only the first step reaction but also the second. The order of reactivity for different solvents was found to be in the sequence as DMF > MeCN > THF > CH 2 Cl 2 > PhMe. Comparing the effect of the solvent on the two-step reaction, MeCN was the most suitable one. We found that Cs 2 CO 3 should be used as the proper base for the first-step reaction instead of stronger bases to avoid the unwanted self-elimination of a-bromo carbonyl compounds. The self-elimination would produce conjugated a,b-unsaturated ketones or esters, es...
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