Albert Cantos

On the regioselectivity of the nucleophilic aromatic photosubstitutions of 4-nitroveratrole. A threefold mechanistic pathway

Abstract 4-Nitroveratrole (NVT) is photosubstituted with primary amines, piperidine and hydroxide ion. Primary amines and hydroxide ion cause replacement of the methoxy group in meta position with respect to the nitro group whereas piperidine photosubstitutes the methoxy group in para to the nitro group. Photoreactions with piperidine and hydroxide ion involve attack of the amine upon a triplet excited state of NVT.Mechanistic evidences indicate that the reaction with hydroxide ion is probably a S N 2 3 Ar * process whereas the reaction with piperidine involves a radical ion pair formed via electron transfer from the amine to a triplet excited state. Photoreactions. with primary amines involve attack of the amine upon a singlet excited state of NVT (S N 2 1 Ar * process). These results are discussed and justified in the context of nucleophile ionization potential considerations and ground state donor-acceptor complex formation abilities.

On the regioselectivity of the nucleophilic aromatic photosubstitution of 4-nitroanisole. A dual mechanistic pathway

Abstract 4-Nitroanisole photoreacts with n -hexylamine and ethyl glycinate giving rise to regioselective methoxy and nitro group photosubstitutions respectively. Mechanistic evidences indicate the last is produced through a S N 2 3 Ar * reaction whereas the first arises from a radical ion pair via electron transfer from the amine to a 4-nitroanisole triplet excited state.

On the regioselectivity of the nucleophilic aromatic photosubstitution. The photoreaction of 4-nitroveratrole with n-hexylamine.

4-Nitroveratrole is photosubstituted with n-hexylamine giving rise to two isomeric anilines, N-hexyl-2-methoxy-5-nitroaniline and N-hexyl-2-methoxy-4-nitroaniline. Mechanistic evidence indicates that the first is produced in an SN2Ar reaction through singlet and triplet excited states, whereas the second arises from a radical ion pair via electron transfer from the amine to a triplet excited state.

Singlet-triplet mechanistic duality in the photosubstitution of nitrophenyl ethers with ethyl glycinate. The role of single electron transfer.

Abstract Mechanistic studies show that 4-nitroveratrole and 4,5-dinitroveratrole undergo nucleophilic aromtic photosubstitution with ethyl glycinate through an SN2Ar* route. However, in the first case the photoreaction takes place through a singlet excited state whereas for 4,5-dinitroanisole a triplet excited state is involved. Electrochemical data for the present photoreactions reagents and for 4-nitroanisole, involved in a related photoreaction previously described by us, are reported. A mechanistic scheme, governed by a direct collapse - electron transfer competition in the singlet excited state stage, is proposed for the nucleophilic aromatic photosubstitution reactions of nitrophenyl ethers with amine nucleophiles.

The Search for Biochemical Photoprobes. III. The Photoreactions of 4-Nitroveratrole and 2-Fluoro-4-nitroanisole with Bovine Pancreatic Ribonuclease A and with Model Nucleophiles.

Abstract The photoreactions of 4-nitroveratrole (NVT) and 2-fluoro-4-nitroanisole (FNA) with bovine pancreatic ribonuclease A (RNAase A) and with model nucleophiles are described. From them it is concluded that 2-fluoro-4-nitrophenyl ethers constitute improved alternative biochemical photoprobes, specially for proteins where a number of good nucleophiles are present.

The search for new biochemical photoprobes. II. The nucleophilic photosubstitution of 2-fluoro-4-nitroanisole.☆

Abstract The photosubstitutions of 2-fluoro-4-nitroanisole with several amines are studied. The preparative results, the thermal stability of the photochemical substrate, and the limiting quantum yield values obtained from photoreactions with several nucleophiles suggest the possible usefulness of 2-fluoro-4-nitrophenyl ethers as biochemical photoprobes.

Synthesis and photochemical reactions of nitroestrogens: Possible photoaffinity labels of zero length

The syntheses of 3,4-dimethoxy-1,3,5(10)-estratrien-17-one and 4-bromo-3-methoxy-2-nitro-1,3,5(10)-estratrein-17-one are described and their photoreactions with amines and hydroxide ion studied. The possible usefulness of these new steroids as photoaffinity labels of zero length is discussed.