Newman–Kwart rearrangement

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Newman-Kwart rearrangement
Named after Melvin Spencer Newman
Harold Kwart
Reaction type Rearrangement reaction
Identifiers
Organic Chemistry Portal newman-kwart-rearrangement
RSC ontology ID RXNO:0000412

The Newman–Kwart rearrangement is a type of

migrates from the oxygen atom to the sulfur atom, forming an S-aryl thiocarbamate, ArSC(=O)NMe2.[1][2][3] The reaction is named after its discoverers, Melvin Spencer Newman[4] and Harold Kwart.[5] The reaction is a manifestation of the double bond rule. The Newman–Kwart reaction represents a useful synthetic tool for the preparation of thiophenol
derivatives.

Mechanism

The Newman–Kwart rearrangement is intramolecular. It is generally believed to be a concerted process, proceeding via a four-membered cyclic transition state (rather than a two-step process passing through a discrete reactive intermediate).[3][6] The enthalpy of activation for this transition state is generally quite high for typical substrates (ΔH‡ ~ 30 to 40 kcal/mol), necessitating high reaction temperatures (200 to 300 °C, Ph2O as solvent or neat).[7]

A Pd-catalyzed process[2] and conditions under photoredox catalysis[8] (both proceeding through complex multistep mechanisms) are known. These catalytic processes allow for much milder reaction conditions to be used (100 °C for Pd catalysis, ambient temperature for photoredox).

Use for preparation of thiophenols

The Newman–Kwart rearrangement is an important prelude to the synthesis of

thiocarbamoyl chloride (2) to form an O-aryl thiocarbamate (3). Heating 3 to around 250 °C causes it undergo Newman–Kwart rearrangement to an S-aryl thiocarbamate (4). Alkaline hydrolysis or similar cleavage yields a thiophenol (5).[6][9]

See also

References

  1. PMID 23605512
    .
  2. ^
    PMID 19746383
    .
  3. ^
    doi:10.1055/s-2008-1032179
    .
  4. doi:10.1021/jo01350a023
    .
  5. doi:10.1021/jo01340a015
    .
  6. ^
    PMID 20812755
    .
  7. doi:10.1139/v06-161
    .
  8. ISSN 0002-7863
    .
  9. doi:10.15227/orgsyn.051.0139
    .
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