Efficient stereoselective nucleophilic addition of pyrroles to chiral nitrones

Abstract

Regioselective additions of pyrroles to a variety of optically active nitrones under smooth acidic conditions lead to chiral pyrrolic N-hydroxylamines in good to excellent yields. Depending on the position of the chirality on the nitrone partner, the addition products have been isolated with high diastereoselectivity levels. Reaction of glyoxylate based chiral nitrones either at the C-2 or at the C-3 position of the pyrrole nucleus afforded N-hydroxyamino esters in high yields as single diastereoisomers. These adducts allow access to enantio-enriched non proteinogenic 2'- and 3'-pyrrolylglycines (13 and 19 respectively).

Spin transition triggered by desorption of crystal solvents for a two-dimensional cobalt(ii) complex with hydrogen bonding

“…Three NOH sites, N4-O1, N5-O2 and N9-O3, have N-O bond lengths of 1.432(9), 1.48(2) and 1.447(10) Å, respectively, which are close to those established in previous work (1.451-1.497 Å). [30][31][32][33][34][35] On the other hand, the N10-O4 bond length of 1.396(15) Å is close to that of a polarized form (>N + -O -) of 1.4170(15) Å. 36 The polarization at the N10-O4 site could be related to the intermolecular contact.…”

Concise Preparation of Optically Active Heteroaryl α‐(Hydroxyamino) Esters

“…Owing to the lower reactivity of the C‐3 position of the pyrrole ring, an increase in the reaction temperature was suitable to obtain 3d in 86 % yield starting from pyrrole 1d (Table 1, Entries 3 and 4). Hydroxylamine 3e was also obtained by using the previously described conditions 14. As it was initially observed with 3a , products 3b – e were all obtained as single diastereoisomers.…”

“…The addition of pyrrole ( 1a ) to cyclic chiral nitrone ( R )‐ 2 13 was highly diastereoselective and led to the exclusive formation of (3 R ,5 R )‐ 3a in 76 % yield 14. Compound 3a was next converted into α‐(hydroxyamino) ester 6a in only a few steps (Scheme ).…”

Visible-light-promoted nitrone synthesis from nitrosoarenes under catalyst- and additive-free conditions

“…Under transition metal catalytic conditions, they can also be used as directing groups to realize sp 2 C-H activation reactions [15,16]. In addition, many others useful reaction types of nitrones are developed in the past several years [17][18][19][20][21].…”