Vinylphosphonium Salt Mediated Reaction between Alkyl Propiolates and Aminophenols or Hydroxyphenols

Abstract

Addition of catechol to methyl propiolate or ethyl phenylpropiolate in the presence of Ph 3 P leads to methyl 2-(1,3-benzodioxol-2-yl)acetate or 3-(1-phenylmethylidene)-1,4-benzodioxin-2-one. 2-Aminophenols react with alkyl propiolates in the presence of Ph 3 P to produce a nearly 1:1 mixture of 3-methyl-2H-1,4-benzoxazin-2-one derivatives and methyl (E)-3-(2-aminophenoxy)-2-propenoates.

Preparation of 2H‐1,4‐Benzoxazin‐2‐one Derivatives under Heterogeneous Conditions via Domino Process

“…Compared with other reported procedures, [11][12][13][14] our approach shows higher eco-sustainability thanks to the use of the solid supported promoter. In fact the use of solvents is minimized, reducing the classical tedious work-up to an easy filtration and evaporation.…”

“…b-Nitroacrylates are an emerging class of functionalized nitroalkenes that show high chemical versatility since they have been employed as strategic starting materials for the preparation of a variety of fine chemicals [8] and natural products. [9] Benzoxazines constitute a class of compounds of important biological interest, [10] in particular, 1,4-benzA C H T U N G T R E N N U N G oxazin-2-one structures, usually synthesized by the reaction between o-aminophenols with a-keto esters [11][12][13] or alkyl propriolates, [14] are of great interest due to both their photochemical activity [11,15] and their presence in many important products such as cephalandole alkaloids, [16] analogues of squamocin, [17] drugs (such as psoralen plus UVA). [13] A plausible mechanism of our reaction consists in a domino process in which four different transformations are involved: (i) hetero-Michael addition of the amine functionality to nitroolefins giving the intermediates 3, (ii) intramolecular transesterification with formation of 4, (iii) elimination of a molecule of nitrous acid affording the intermediates 5, and (iv) [1,3]-proton shift with the formation of target products 6, as previously reported in the literature.…”

“…[13] A plausible mechanism of our reaction consists in a domino process in which four different transformations are involved: (i) hetero-Michael addition of the amine functionality to nitroolefins giving the intermediates 3, (ii) intramolecular transesterification with formation of 4, (iii) elimination of a molecule of nitrous acid affording the intermediates 5, and (iv) [1,3]-proton shift with the formation of target products 6, as previously reported in the literature. [14] With the view to optimizing the process, we investigated the reaction using stoichiometric amounts of bnitroacrylate 1a and 2-aminophenol 2a, in ethyl acetate as eco-friendly solvent, [18] under different conditions. Thus, as reported in Table 1, the best result was obtained in the presence of an equimolar amount of carbonate on polymer, at 55 8C for 5.5 h (entry b), however, a comparable result was also obtained at 35 8C after 24 h (entry a).…”

Organocatalytic transformations of alkynals, alkynones, propriolates, and related electron-deficient alkynes

“…53 The ratio was dependent on the nature of the 2-aminophenol and the starting propiolate 105 (with or without substituent). Interestingly, the a-addition of alcohols was reported by Tebby and co-workers more than 40 years ago.…”

“…53 Recently, Kwon and co-workers have reported the formation of functionalized alkylidene phthalans through tandem Michael-Heck reactions from benzyl alcohols 143. The phosphine possessed a dual role in this tandem transformation; first acting as a nucleophilic catalyst in the Michael addition, and then as a ligand for the palladium catalyst (Scheme 64).…”