Structural Feature

Experimental Implication

Role in Route Design

Linear C4 backbone

Provides a four-carbon linker of fixed length

Suitable for side-chain designs that require control over the spacing of a “butyl/hydroxybutyl” unit

Free hydroxyl group at one terminus

Can preferentially undergo oxidation, esterification, sulfonylation, or related transformations

Allows early-stage transformations to be focused on one clearly defined site

TBS-protected hydroxyl group at the other terminus

Remains temporarily unreactive in the early stage and can be released later

Facilitates stepwise management of the current reaction site and the downstream functional site

Current Experimental Objective

Worth Prioritizing?

Basis for the Judgment

A C4 linker of fixed length is required, and the terminal hydroxyl must still be released at a later stage

Yes, worth prioritizing

A single molecule addresses both chain-length definition and site differentiation

Oxidation, substitution, or leaving-group installation is intended first, with hydroxyl unveiling deferred to a later stage

Yes, worth prioritizing

The free terminus and the protected terminus have clearly differentiated roles, giving a well-organized route sequence

Only a simple butanediol fragment is needed, and simultaneous exposure of both hydroxyl groups is not problematic

Not necessary to prioritize

Direct use of 1,4-butanediol is usually more straightforward

Subsequent steps will enter conditions unfavorable for TBS retention at an early stage

Requires careful evaluation

The protecting group may fail prematurely, weakening its value for route organization

The target does not require a flexible C4 chain, but instead a shorter, longer, or more rigid linker

Another building block should be chosen

The advantage of this molecule depends on matching the butylene chain length to the synthetic task

Experimental Task

Key Early-Stage Transformation

Role in the Route

Experimental Points Requiring Special Attention

Oxidation to the aldehyde followed by further elaboration

Oxidation of the free terminus to the corresponding aldehyde

One terminus enters carbonyl chemistry, while the other remains as a hydroxyl site that can be released later

Avoid overoxidation, and ensure compatibility between downstream addition, condensation, or reductive amination conditions and retention of the TBS group

Conversion to a leaving group followed by substitution

Conversion of the free terminus into a mesylate, tosylate, halide, or another leaving group

Transforms the intermediate into a C4 linker fragment bearing a protected terminal hydroxyl group

Prevent elimination and hydrolytic side reactions, and evaluate the impact of subsequent nucleophilic substitution conditions on the TBS group

Incorporation as a protected hydroxybutyl fragment into a larger skeleton

Retention of the TBS terminus during intermediate-stage assembly

Complete skeleton construction first, then decide when to release the terminal hydroxyl group

Plan the desilylation stage in advance to avoid premature hydroxyl exposure under acidic or fluoride-containing conditions

Consideration

What to Evaluate

Impact on Route Selection

Need for early-stage stability

Whether an unreactive hydroxyl site needs to be retained during the early stage

If yes, the TBS-protected terminus is more valuable

Need for late-stage release

Whether the terminal hydroxyl group must be regenerated later

If yes, the TBS-protected terminus is suitable as a latent hydroxyl site

Compatibility with downstream conditions

Whether later steps will encounter fluoride-containing, acidic, or Pd/C-methanol hydrogenation conditions that may also promote TBS removal at an early stage

If yes, the design value of the TBS-protected terminus is reduced

Source of the starting building block

Whether this intermediate can be purchased directly or must be prepared by monoprotection of 1,4-butanediol

If it must be prepared in-house, monoprotection selectivity, the separation burden from unreacted diol and bis-protected byproducts, yield, purification cost, and practicality on scale should all be included in the comparison

Research or Experimental Objective

Which Table to Read First

Why Start with This Table

Which Other Table(s) to Read Together

Purpose of Cross-Referencing

To first clarify which core building blocks define this route, including the upstream starting material, the target monoprotected intermediate, and the corresponding aldehyde intermediate

Table 1

Table 1 brings together 1,4-butanediol, the monoprotected C4 building block, and its corresponding aldehyde intermediate, making it easier to judge whether the route is organized around the monoprotected diol building block or extended further from the aldehyde intermediate

Tables 2 and 3

Table 2 supplements the conditions for establishing single-end TBS protection, and Table 3 supplements oxidation conditions for converting the free terminus into the aldehyde

To establish the basic conditions for a “free hydroxyl at one end + TBS protection at the other end” starting from 1,4-butanediol

Table 2

Table 2 focuses on TBS installation reagents and their supporting base systems, making it suitable for first judging whether single-end protection can be established, whether the conditions are clean, and whether they are suitable for later scale-up

Table 1

Table 1 helps determine the position of this monoprotected intermediate within the overall route and whether, once established, it should be used directly or further converted into the corresponding aldehyde intermediate

To compare conventional TBS installation with high-activity TBS installation and judge substrate compatibility and reaction efficiency

Table 2

Table 2 contains both conventional silylation reagents and more reactive silylation reagents, along with different types of organic bases, allowing comparison of reactivity, steric compatibility, and condition mildness

Table 1

Table 1 helps determine whether this protection step is meant to support subsequent use of the building block or whether a different starting material should be considered directly

To oxidize the free hydroxyl terminus to the aldehyde first, then continue with condensation, nucleophilic addition, or reductive amination

Table 3

Table 3 focuses on common oxidation systems for converting a primary alcohol at the free terminus into the aldehyde, making it suitable for first judging whether the corresponding aldehyde can be obtained reliably and which oxidation conditions best match the current substrate

Table 1

Table 1 helps confirm the position of the corresponding aldehyde within the overall route and arrange the subsequent bond-forming or side-chain extension steps

To compare hypervalent iodine, chromium-free, chromium-based, and low-temperature oxidation pathways in order to judge which system is more suitable for the current substrate

Table 3

Table 3 places different types of oxidation systems side by side, allowing horizontal comparison in terms of functional-group tolerance, operational conditions, workup burden, and scale-up convenience

Table 4

Table 4 supplements late-stage hydroxyl activation, coupling, and TBS deprotection conditions, helping coordinate compatibility between early-stage oxidation and later-stage steps

To convert the free hydroxyl terminus into a tosylate or another leaving group for subsequent nucleophilic substitution or terminal functional-group replacement

Table 4

Table 4 focuses on hydroxyl-activation reagents and is suitable for first establishing a route in which the free terminus is converted into a leaving site before the C4 fragment is brought into another skeleton

Table 1

Table 1 helps judge whether this route is better suited to using the building block as a C4 linker fragment bearing a protected terminal hydroxyl group, rather than following the oxidation-to-aldehyde pathway

To convert the free hydroxyl terminus into a carbonate-type activated intermediate and then connect it with an amine, alcohol, or a more complex skeleton

Table 4

Table 4 focuses on common activation reagents for carbonate/carbamate-type coupling and is suitable for first judging which hydroxyl-activation pathway is more appropriate for the free terminus

Table 2

Table 2 supplements early-stage TBS installation conditions and base-system information to help judge whether these factors may affect subsequent hydroxyl activation and coupling performance

To release the TBS-protected terminus selectively at a later stage and convert the latent hydroxyl group back into a reactive site

Table 4

Table 4 presents different TBS deprotection conditions, making it suitable for comparing release efficiency, substrate tolerance, and effects on other functional groups

Tables 1 and 3

Table 1 helps judge the role of the released hydroxyl group within the overall route, and Table 3 helps assess whether this deprotection step remains compatible after early-stage oxidation

To judge whether this route is better suited to “protect first, then oxidize” or to “retain the free terminus and proceed through activation/coupling”

Table 1

Table 1 first clarifies the relationships among the key intermediates, making it easier to judge whether the target task is more oriented toward aldehyde-based extension or overall linker-fragment introduction

Tables 3 and 4

Table 3 corresponds to routing the free terminus into carbonyl chemistry, while Table 4 corresponds to free-terminus activation, coupling, and late-stage release; together they supplement condition evaluation for different route branches

To build a transferable linker-screening framework around this type of monoprotected diol building block

Table 1

Table 1 helps first define the core features of this type of building block, namely the relationship among the C4 backbone, single-end protection, and the single-end operable site

Tables 2–4

Table 2 supplements protection establishment, Table 3 supplements elaboration by free-terminus oxidation, and Table 4 supplements activation, coupling, and late-stage release; together they are more useful for establishing a complete screening framework

Classification

CAS No.

Aladdin Catalog No.

Name

Specification or Purity

Product Features and Applications

Upstream C4 diol precursor

110-63-4

B1508458

1,4-Butanediol (BDO)

Anhydrous grade, ≥99%

A direct upstream starting material for constructing a monoprotected C4 linker. It is suitable for selective monosilylation first, while keeping the other terminus available for subsequent oxidation, activation, or coupling.

Core monoprotected C4 building block

87184-99-4

D136918

4-(tert-Butyldimethylsilyl)oxy-1-butanol

≥97%

A typical monoprotected 1,4-butanediol building block. One terminus retains a free hydroxyl group for initial transformations, while the other is reserved in TBS-protected form for later release, making it suitable for organizing stepwise coupling and downstream elaboration.

Corresponding aldehyde intermediate

87184-81-4

O725176

4-((tert-Butyldimethylsilyl)oxy)butanal

≥95%

The direct intermediate obtained after oxidation of the free terminus of the monoprotected alcohol. It is suitable for further condensation, nucleophilic addition, reductive amination, or side-chain extension.

Classification

CAS No.

Aladdin Catalog No.

Name

Specification or Purity

Product Features and Applications

Auxiliary base/promoter for TBS installation

288-32-4

I432539

Imidazole

Anhydrous grade, ACS, ≥99%

A commonly used auxiliary base and silylation promoter under TBDMSCl conditions. It is suitable for organizing 1,4-butanediol into a route starting point with one protected terminus and one retained terminus.

Acid scavenger base

121-44-8

T140677

Triethylamine

Anhydrous grade, ≥99.5%, Water ≤50 ppm

Commonly used as an acid scavenger in TBS installation, tosylation, and active carbonate construction, helping free-hydroxyl transformations proceed smoothly.

High-reactivity TBS installation reagent

69739-34-0

T485764

tert-Butyldimethylsilyl trifluoromethanesulfonate

Suitable for synthesis

More reactive than TBDMSCl, and suitable for rapid introduction of TBS protection when steric hindrance is high or substrate reactivity is relatively low.

Sterically hindered acid scavenger base

7087-68-5

D109322

N,N-Diisopropylethylamine

Distilled grade, ≥99.5%

A sterically hindered non-nucleophilic organic base suitable for use with highly reactive silylation or hydroxyl-activation systems to reduce unnecessary side reactions.

Nucleophilic catalytic base/acyl-transfer catalyst

1122-58-3

D109207

4-Dimethylaminopyridine

≥99%

Commonly used in active carbonate and acyl-transfer systems, and can also help improve the efficiency of certain alcohol hydroxyl derivatization steps.

Conventional TBS installation reagent

18162-48-6

B103644

Tert-butyldimethylchlorosilane (TBDMSCl)

≥97%

A conventional TBS installation reagent suitable for constructing a C4 linker from 1,4-butanediol with one protected terminus and one synthetically addressable terminus.

Classification

CAS No.

Aladdin Catalog No.

Name

Specification or Purity

Product Features and Applications

Terminal oxidant used with TEMPO

7681-52-9

S101639

Sodium hypochlorite solution

Available chlorine ≥5.0%

Commonly used with TEMPO in catalytic oxidation systems to oxidize the primary alcohol at the free terminus to the aldehyde, facilitating subsequent condensation, reductive amination, or chain extension.

Swern oxidation component

67-68-5

D103280

Dimethyl sulfoxide (DMSO)

Pharmaceutical grade, PharmPure™

In combination with oxalyl chloride, it converts the primary alcohol at the free terminus into the corresponding aldehyde and is suitable for carbonyl-based elaboration while retaining the TBS-protected terminus.

Swern oxidation component

79-37-8

O434200

Oxalyl chloride

Reagent grade, premium grade, ≥99%

A key activating component in the Swern oxidation system, used with DMSO for low-temperature oxidation of the free-terminal alcohol to the aldehyde.

Catalytic oxidant

2564-83-2

T478495

TEMPO

Sublimed grade, ≥99%

A commonly used nitroxyl radical catalyst for oxidation of the primary alcohol at the free terminus, suitable for mild preparation of the corresponding aldehyde while reducing the risk of overoxidation.

Hypervalent iodine oxidant

61717-82-6

I102429

2-Iodoxybenzoic acid

80 wt.%, contains benzoic acid and isophthalic acid stabilizers

Capable of oxidizing the primary alcohol at the free terminus to the aldehyde. Suitable when mild conditions are needed and strongly acidic metal-based oxidation systems are to be avoided.

TPAP co-oxidant

7529-22-8

M105979

4-Methylmorpholine N-oxide (NMO)

50% aqueous solution

A commonly used co-oxidant in TPAP-catalyzed oxidation, employed to regenerate the active ruthenium species and drive oxidation of the free-terminal alcohol to the aldehyde.

Chromium oxidant

26299-14-9

P106557

Pyridinium chlorochromate

≥98%

A classic chromium oxidant that converts the primary alcohol at the free terminus into the aldehyde. It is suitable for comparing reaction performance against DMP, IBX, Swern, or TEMPO systems.

Hypervalent iodine co-oxidant used with TEMPO

3240-34-4

D106797

Iodobenzene diacetate (DIB)

≥98%

Used with TEMPO to form a hypervalent iodine oxidation system suitable for mild oxidation of the primary alcohol at the free terminus to the aldehyde.

Ru oxidant

114615-82-6

T118500

Tetrapropylammonium perruthenate

≥97%

A mild and highly selective ruthenium oxidant suitable for converting the primary alcohol at the free terminus into the aldehyde, and for use with NMO as a chromium-free oxidation comparison.

Mild hypervalent iodine oxidant

87413-09-0

D110230

Dess-Martin Periodinane (DMP)

≥96%

A commonly used mild hypervalent iodine oxidant suitable for converting the primary alcohol at the free terminus into the aldehyde, thereby facilitating subsequent condensation, reductive amination, or chain extension.

Classification

CAS No.

Aladdin Catalog No.

Name

Specification or Purity

Product Features and Applications

Hydroxyl-activation / tosylation reagent

98-59-9

T485782

p-Toluenesulfonyl chloride (PTSC)

Suitable for synthesis

Converts the free hydroxyl group into a tosylate, facilitating subsequent nucleophilic substitution, linker extension, or terminal functional-group replacement.

Mild fluoride source for TBS deprotection

12125-01-8

A431591

Ammonium fluoride

Suitable for analysis, ACS, guaranteed reagent

A relatively mild fluoride source for desilylation, suitable for screening when release of the terminal hydroxyl group is desired but stronger fluoride conditions are not preferred.

Classical fluoride source for TBS deprotection

62778-11-4

H107606

Hydrogen fluoride-pyridine

Pyridine ~30%, hydrogen fluoride ~70%

A classical TBS deprotection reagent, suitable for site-specific late-stage release of the protected hydroxyl group and reconversion of the latent site into a reactive terminus.

Inorganic fluoride source for TBS deprotection

13400-13-0

C755570

Cesium fluoride

UltraBio™, ≥99%(F)

An inorganic fluoride source suitable for removing TBS protection and releasing the terminal hydroxyl group. It can serve as a comparison condition to organic ammonium fluorides.

Classical fluoride source for TBS deprotection

429-41-4

T106821

Tetrabutylammonium fluoride solution (TBAF solution)

1.0 M in THF

One of the commonly used conditions for TBS deprotection, suitable for rapid late-stage release of the terminal hydroxyl group before further esterification, carbonate formation, or coupling.

Carbonyl activation / carbonate-forming reagent

530-62-1

C109315

N,N'-Carbonyldiimidazole (CDI)

≥99%

Can direct the free hydroxyl group into carbonate or carbamate pathways, making it suitable for converting this C4 fragment into an activated intermediate for further coupling with amines or alcohols.

Active carbonate construction reagent

7693-46-1

N159046

4-Nitrophenyl Chloroformate

≥98%(T)

Commonly used to prepare 4-nitrophenyl active carbonates, facilitating subsequent coupling with amines, alcohols, or more complex skeletons.

Active carbonate construction reagent

74124-79-1

D106171

N,N'-Disuccinimidyl Carbonate (DSC)

≥98%

An active carbonate construction reagent suitable for converting the free hydroxyl group into a succinimidyl active carbonate, followed by coupling with amine substrates.