Cyclopropylboronic acid
[CAS 411235-57-9]

Identification

• Classification: Chemical reagent >> Organic reagent >> Boric acid
• Name: Cyclopropylboronic acid
• Molecular Formula: C₃H₇BO₂
• Molecular Weight: 85.90
• CAS Registry Number: 411235-57-9
• EC Number: 609-890-0
• SMILES: B(C1CC1)(O)O

Properties

• Density: 1.1±0.1 g/cm³ Calc.^*
• Melting point: 90 - 95 °C (Expl.)
• Boiling point: 205.1±23.0 °C 760 mmHg (Calc.)^*
• Flash point: 77.9±22.6 °C (Calc.)^*
• Index of refraction: 1.443 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS02;GHS05;GHS07;GHS08 Danger
• Risk Statements: H242-H302-H315-H318-H319-H335-H360
• Safety Statements: P203-P210-P234-P235-P240-P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P305+P354+P338-P317-P318-P319-P321-P330-P332+P317-P337+P317-P362+P364-P370+P378-P403-P403+P233-P405-P410-P411-P420-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	4	H302
Self-reactive substances or mixtures	Self-react.	C	H242
Serious eye damage	Eye Dam.	1	H318
Reproductive toxicity	Repr.	1B	H360
Self-reactive substances or mixtures	Self-react.	E	H242

chemBlink Chemical Story

Cyclopropylboronic acid is an organoboron compound that has become one of the standard building blocks in modern synthetic and medicinal chemistry. Although structurally simple, its scientific importance extends far beyond its molecular composition. It represents the convergence of two major developments in late twentieth-century chemistry: the emergence of Suzuki-Miyaura cross-coupling as a general carbon-carbon bond-forming reaction and the growing recognition of the cyclopropyl group as a valuable structural motif in pharmaceutical design.

The transformation of organic synthesis began in 1979 when Akira Suzuki and co-workers demonstrated that organoboron compounds could undergo palladium-catalyzed cross-coupling with organic halides under relatively mild conditions. Compared with many other organometallic reagents, boronic acids offered significant advantages, including good stability, broad functional-group compatibility, and generally low toxicity. Suzuki-Miyaura coupling rapidly became one of the most versatile methods for constructing carbon-carbon bonds and is now among the most frequently employed reactions in pharmaceutical and fine chemical synthesis.

At approximately the same time, medicinal chemists discovered that the cyclopropyl group possessed properties extending well beyond its small size. Despite containing only three carbon atoms, its highly strained ring influences molecular shape, conformational flexibility, lipophilicity, and metabolic behavior. Replacing an alkyl substituent with a cyclopropyl group often improves metabolic stability or alters interactions with biological targets, making cyclopropyl substitution an increasingly common strategy in lead optimization. Numerous antibacterial, antiviral, anticancer, and central nervous system agents now incorporate cyclopropyl groups as key structural elements.

Cyclopropylboronic acid provided an efficient solution for introducing this valuable fragment into aromatic and heteroaromatic molecules. Through Suzuki-Miyaura coupling, chemists can readily attach a cyclopropyl group to a wide variety of halogenated substrates under conditions compatible with many sensitive functional groups. As a result, the reagent has become a routine intermediate in medicinal chemistry laboratories, where rapid preparation of compound libraries is essential for structure-activity relationship studies.

Beyond pharmaceutical research, cyclopropylboronic acid is also employed in the synthesis of agrochemicals, functional organic materials, and research compounds. Its reliability, commercial availability, and compatibility with automated parallel synthesis have further strengthened its role in modern discovery chemistry. Like many organoboron reagents, it illustrates how standardized synthetic building blocks can dramatically accelerate molecular innovation by allowing chemists to assemble complex structures from readily available components.

The scientific significance of cyclopropylboronic acid therefore lies not in a single end product but in the synthetic strategy it enables. By combining the unique biological advantages of the cyclopropyl group with the versatility of Suzuki-Miyaura coupling, it has become one of the classic cross-coupling building blocks of contemporary medicinal chemistry. Its widespread use reflects the broader evolution of organic synthesis toward modular, efficient, and highly adaptable molecular construction.

**References**

1. Miyaura, N.; Suzuki, A. (1995). "Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds." *Chemical Reviews*, 95, 2457-2483.

2. Suzuki, A. (2011). "Cross-Coupling Reactions of Organoboranes: An Easy Way to Construct C-C Bonds." *Angewandte Chemie International Edition*, 50, 6722-6737.

3. Talele, T. T. (2016). "The 'Cyclopropyl Fragment' Is a Versatile Player That Frequently Appears in Preclinical and Clinical Drug Molecules." *Journal of Medicinal Chemistry*, 59, 8712-8756.