Spiro[indoline-3,2'-[1,3]dioxolan]-2-one: Properties & Lab Guide

Spiro[indoline-3,2'-[1,3]dioxolan]-2-one is a structurally distinctive spiro heterocyclic compound in which the C-3 carbonyl of isatin is protected as a cyclic 1,3-dioxolane ketal while retaining the lactam carbonyl at C-2, making it a versatile building block for the synthesis of biologically relevant oxindole and spiro-oxindole frameworks.

IUPAC Name

Spiro[indoline-3,2'-[1,3]dioxolan]-2-one

Aladdin SKU

S697104

Molecular Formula

C9H7NO3

Molecular Weight

177.16 g/mol

Core Scaffold

Spiro-fused oxindole–1,3-dioxolane

Primary Function

Ketal-protected isatin derivative; synthetic intermediate

Recommended Storage

Cool, dry, well-ventilated location away from light

Chemical Identity and Structure

Spiro[indoline-3,2'-[1,3]dioxolan]-2-one (Aladdin SKU S697104) belongs to the family of spiro-fused heterocyclic compounds. Its structure is best understood as the cyclic ethylene ketal of isatin (1H-indole-2,3-dione): the electrophilic C-3 ketone of isatin is condensed with ethylene glycol to form a five-membered 1,3-dioxolane ring, generating a spiro centre at C-3. The C-2 lactam carbonyl of the oxindole ring remains intact and free for further chemical manipulation.

Molecular formula: C₉H₇NO₃; molecular weight: 177.16 g/mol. The compound is a white to off-white solid under ambient conditions. The presence of the protected ketone alongside the lactam creates orthogonal reactivity, enabling selective transformations at each functional group in multi-step synthetic sequences.

Research Applications

The selective protection of the C-3 carbonyl of isatin as a 1,3-dioxolane ketal is a widely employed strategy in the preparation of spiro-oxindole natural product analogues and pharmaceutical candidates. Spiro[indoline-3,2'-[1,3]dioxolan]-2-one serves as a key intermediate in several synthetic contexts:

• Spiro-oxindole synthesis: The protected C-3 position prevents undesired side reactions during manipulation of the C-2 lactam, allowing selective N-alkylation, N-acylation, or reduction of the amide.
• Medicinal chemistry: Spiro-oxindole motifs are present in a range of bioactive natural products and drug candidates with reported antimicrobial, anticancer, and enzyme-inhibitory activities. This compound provides a stable, isolable intermediate toward such targets.
• Functional group interconversion: After modification at C-2, the ketal can be hydrolysed under mild acidic aqueous conditions to regenerate the isatin ketone, enabling further elaboration such as Wittig olefination or nucleophilic addition.
• Diversity-oriented synthesis (DOS): The compound is a useful scaffold for building compound libraries via reactions at the lactam nitrogen and the ketal carbon.

Handling, Safety, and Storage

Although Spiro[indoline-3,2'-[1,3]dioxolan]-2-one is not classified as a highly hazardous material at the research scale, standard laboratory safety practices must be observed:

• Personal Protective Equipment (PPE): Wear appropriate chemical-resistant gloves, safety goggles, and a laboratory coat when weighing or handling the compound. Work in a well-ventilated area or fume hood to minimise dust or vapour inhalation.
• Storage: Store in a tightly sealed container in a cool, dry, and well-ventilated location, protected from light and moisture. Avoid storage near strong oxidising agents or strong bases, which could promote hydrolysis of the dioxolane ring.
• Stability: The cyclic ketal is susceptible to hydrolysis under strongly acidic or aqueous conditions. Ensure containers are properly sealed after each use to prevent moisture ingress.
• Disposal: Dispose of waste material in accordance with local institutional and regulatory guidelines for organic laboratory chemicals.

Note: Consult the Safety Data Sheet (SDS) provided by Aladdin Scientific for comprehensive hazard information before use.

Practical Synthesis Tips

Researchers incorporating Spiro[indoline-3,2'-[1,3]dioxolan]-2-one into multi-step syntheses should consider the following practical points:

• Ketal formation from isatin: This compound is typically prepared by refluxing isatin with ethylene glycol in the presence of an acid catalyst (e.g., p-toluenesulfonic acid) in toluene with azeotropic removal of water. Starting from the Aladdin-supplied compound avoids this step entirely.
• Solubility: The compound shows good solubility in common polar aprotic solvents such as DMF, DMSO, and acetonitrile, and moderate solubility in dichloromethane and ethyl acetate. Solubility in water is limited.
• Ketal deprotection: Regeneration of the C-3 ketone can be achieved with dilute aqueous acid (e.g., 10% HCl or oxalic acid solution) at room temperature to mild heating; monitor by TLC or LC-MS to avoid over-reaction.
• Lactam reactivity: N-H of the lactam can be alkylated using standard conditions (base such as K₂CO₃ in DMF, alkyl halide) without disturbing the ketal, providing N-substituted intermediates for further diversification.

Frequently asked questions

What is the difference between Spiro[indoline-3,2'-[1,3]dioxolan]-2-one and isatin?

Isatin (1H-indole-2,3-dione) contains two carbonyl groups at C-2 and C-3. Spiro[indoline-3,2'-[1,3]dioxolan]-2-one is the cyclic ethylene ketal derivative of isatin in which the C-3 ketone has been protected as a 1,3-dioxolane, leaving only the C-2 lactam carbonyl available for reaction. This selective protection enables chemists to manipulate the C-2 carbonyl independently.

How should I deprotect the ketal group to regenerate the isatin ketone?

The 1,3-dioxolane ketal can be hydrolysed under mild acidic aqueous conditions. A commonly employed approach is treatment with dilute hydrochloric acid (e.g., 10% aqueous HCl) or a solution of oxalic acid in aqueous acetone at room temperature or with gentle warming. Reaction progress should be monitored by TLC or LC-MS to ensure complete deprotection without degradation of the product.

What solvents are suitable for dissolving Spiro[indoline-3,2'-[1,3]dioxolan]-2-one?

The compound shows good solubility in polar aprotic solvents such as DMF, DMSO, and acetonitrile, and moderate solubility in dichloromethane and ethyl acetate. Aqueous solubility is limited, and prolonged exposure to acidic aqueous media should be avoided to prevent hydrolysis of the dioxolane ring.

Is Spiro[indoline-3,2'-[1,3]dioxolan]-2-one stable at room temperature?

Under dry conditions and away from acidic environments, the compound is generally stable at room temperature for short-term handling. For long-term storage, it is recommended to keep the compound in a tightly sealed container in a cool, dry, and light-protected location to prevent moisture-induced hydrolysis of the ketal.

References

1. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 4th ed.; Wiley: New York, 1992. (General reference for ketal protection of carbonyl compounds.)
2. Galliford, C. V.; Scheidt, K. A. Pyrrolidinyl-spirooxindole natural products as inspirations for the development of potential therapeutic agents. Angew. Chem. Int. Ed. 2007, 46, 8748–8758. doi:10.1002/anie.200701342
3. Jiang, X.; Wang, R. Recent developments in catalytic asymmetric construction of oxindoles and spirooxindoles. Chem. Rev. 2013, 113, 5515–5546. doi:10.1021/cr300374j

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