Cyclopropyl Building Blocks for Organic Synthesis,139.Ethyl Cyclopropylidenepyruvate as a Novel Multifunctional Cyclopropyl Building Block: Facile Preparation and Basic Reaction Patterns

摘要

Tin(II) chloride-mediated Barbier-type coupling of ethyl glyoxylate with 2,3-dibromopro-pene followed by Simmons-Smith cyclopropanation and subsequent Dess-Martin oxidation,afforded ethyl 3-(l-bromocycloprop-l-yl)-2-oxopropionate (5),a stable precursor of ethyl cyclopropylidenepyruvate (1j),in good overall yield (65%),even on a multi-gram scale.The potentially rich chemistry of this novel cyclopropyl building block was illustrated by some basic transformations such as Michael additions of N-,S-,O-and C-nucleophiles (10-91% yields),Diels-Alder reactions with cyclopentadiene (65%) and 2,3-dimethylbuta-l,3-diene (66%) as well as [4+2] cycloadditions across the enone moiety of lj (hetero-Diels-Alder reactions) with furan and enol ethers (65-79%),thus opening up a ready access to a wide range of new variously functional-ized cyclopropane derivatives.