# Solvent- and Electrolyte-Dependent Highly Selective Electrochemical Transfer Hydrogenation of Pyrazolo[1,5-]pyrimidines.
> ピラゾロ[1,5-a]ピリミジンの電気化学的移送水素化における溶媒・電解質依存性の高選択性反応


## Abstract

This study reports the first electrochemical protocols for selective transfer hydrogenation of polynitrogen aromatic heterocycles, specifically pyrazolo[1,5-a]pyrimidines, using water as the hydrogen donor rather than alkali metal hydrides or molecular hydrogen gas. When a MeCN/water mixture with NH4Cl as the supporting electrolyte was employed at 30 °C, regioselective reduction of the C6–C7 double bond was achieved. Switching to a DMSO/water system with Bu4NBF4 enabled reduction of both the C6–C7 double bond and the N4–C5 imine bond. In both cases, unsaturated bonds within the pyrazole ring remained unaffected. The selectivity differences were attributed to the greater reducing capacity of DMSO relative to MeCN and to the stronger interaction of ammonium cations from NH4Cl with the nitrogen lone pairs compared to tetrabutylammonium cations. The approach offers an environmentally compatible alternative to conventional hydrogenation methods.

### Mechanism

Selectivity is governed by two factors: DMSO's stronger reducing capacity compared to MeCN, and the preferential interaction of ammonium cations (NH4Cl) with nitrogen lone pairs in the heterocycle, which differs from the weaker interaction of tetrabutylammonium cations.

## Bibliographic

- **Authors**: Malo S, Das K, Das I
- **Journal**: J Org Chem
- **Year**: 2026 (2026-02-27)
- **PMID**: [41678783](https://pubmed.ncbi.nlm.nih.gov/41678783/)
- **DOI**: [10.1021/acs.joc.5c03069](https://doi.org/10.1021/acs.joc.5c03069)
- **Study type**: other
- **Delivery route**: not specified
- **Effect reported**: not assessed

## Delivery context

The delivery route is not clearly identifiable from this paper. For hydrogen intake, inhalation is the most efficient route; inhalation, however, carries explosion risk (empirical LFL of 10%; high-concentration devices are not recommended).

## Safety notes

The delivery route is not clearly identifiable from this paper. For hydrogen intake, inhalation is the most efficient route; inhalation, however, carries explosion risk (empirical LFL of 10%; high-concentration devices are not recommended).

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)

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> **Cite as**: H2 Papers — PMID 41678783. https://h2-papers.org/en/papers/41678783
> **Source**: PubMed PMID [41678783](https://pubmed.ncbi.nlm.nih.gov/41678783/)