Remote substituent effects on phenylchlorocarbene C-H insertion reactions

Area of Science:

• Organic Chemistry
• Reaction Mechanisms
• Computational Chemistry

Background:

• Carbenes are highly reactive intermediates crucial in organic synthesis.
• Understanding carbene insertion reactions into C-H bonds provides insights into reaction mechanisms.
• Adamantane derivatives offer a rigid framework to study substituent effects on reactivity.

Purpose of the Study:

• To investigate the insertion of phenylchlorocarbene into tertiary C-H bonds of substituted adamantanes.
• To correlate the observed reaction rates with electronic properties of substituents on the adamantane.
• To validate computational methods for predicting carbene insertion reactivity.

Main Methods:

• Experimental determination of relative and absolute rate constants for phenylchlorocarbene insertion.
• Synthesis of 1,3-dimethyladamantane and various 1-X-adamantanes (X = H, OMe, COOMe, Cl, CN).
• Density functional theory (DFT) calculations using the B3LYP/6-31G* level of theory.

Main Results:

• Phenylchlorocarbene successfully inserted into tertiary C-H bonds of all tested adamantane derivatives.
• A strong linear correlation was observed between relative rate constants and inductive substituent constants (sigma1), with rho = -1.5.
• Absolute rate constants varied from 2.5 x 10(5) M(-1) s(-1) for 1,3-dimethyladamantane to 2.5 x 10(4) M(-1) s(-1) for 1-cyanoadamantane.

Conclusions:

• The insertion reactivity of phenylchlorocarbene is significantly influenced by the electronic nature of substituents on the adamantane cage.
• Inductive effects play a dominant role in modulating the carbene insertion rates.
• B3LYP/6-31G* calculations accurately predict the observed reactivity trends, supporting their utility in studying carbene chemistry.