Remote Asymmetric Induction Using Acetate-Type Vinylketene Silyl N,O-Acetals

Area of Science:

• Organic Chemistry
• Asymmetric Synthesis
• Stereoselective Reactions

Background:

• The vinylogous Mukaiyama aldol reaction is a key carbon-carbon bond-forming reaction.
• Achieving remote asymmetric induction in such reactions remains a synthetic challenge.
• Chiral auxiliaries are crucial for controlling stereochemistry in organic synthesis.

Purpose of the Study:

• To develop a method for remote asymmetric induction in the vinylogous Mukaiyama aldol reaction.
• To utilize a novel acetate-type vinylketene silyl N,O-acetal with a chiral auxiliary.
• To achieve selective synthesis of stereochemically defined adducts.

Main Methods:

• Employing an acetate-type vinylketene silyl N,O-acetal derived from crotonate and L-valine.
• Utilizing Lewis acids, specifically tin tetrachloride (SnCl4) and boron trifluoride etherate (BF3·OEt2), for catalysis.
• Investigating the stereochemical outcomes of the reaction under different Lewis acid conditions.

Main Results:

• Selective formation of O-silylated 5R- and 5S-adducts was achieved by using SnCl4 and BF3·OEt2, respectively.
• SnCl4 mediated an isomerization of the silyl dienol ether intermediate.
• The major isomer formed demonstrated high reactivity and yielded the gamma-adduct with excellent stereoselectivity.

Conclusions:

• Remote asymmetric induction is feasible in vinylogous Mukaiyama aldol reactions using the developed chiral auxiliary system.
• The choice of Lewis acid dictates the stereochemical outcome (5R or 5S adduct).
• The observed isomerization and subsequent high stereoselectivity highlight the reaction's potential for complex molecule synthesis.