The Lossen rearrangement from free hydroxamic acids

Area of Science:

• Organic Chemistry
• Reaction Mechanisms
• Synthetic Chemistry

Background:

• The Lossen rearrangement, a classic organic reaction, transforms hydroxamic acids into isocyanates.
• Historically, this transformation required stoichiometric activating reagents for dehydrating primary hydroxamic acids.
• Recent breakthroughs enable the Lossen rearrangement directly from free hydroxamic acids, revitalizing research interest.

Purpose of the Study:

• To review recent advancements in the Lossen rearrangement reaction.
• To highlight new methodologies enabling direct conversion from free hydroxamic acids.
• To provide insights into the mechanisms of various Lossen rearrangement pathways.

Main Methods:

• Summarizing literature on metal-assisted Lossen rearrangement.
• Describing self-propagative Lossen rearrangement mechanisms.
• Reviewing promoted self-propagative Lossen rearrangement strategies.

Main Results:

• Demonstration of Lossen rearrangement occurring directly from free hydroxamic acids.
• Elucidation of mechanisms for metal-assisted, self-propagative, and promoted self-propagative pathways.
• Highlighting the renewed potential of the Lossen rearrangement in organic synthesis.

Conclusions:

• The Lossen rearrangement has evolved beyond its traditional requirements.
• Direct conversion from free hydroxamic acids represents a significant advancement.
• Understanding the mechanisms is key to unlocking new synthetic applications.