Highly stereoselective iodolactonization of 4,5-allenoic acids--an efficient synthesis of 5-(1'-iodo-1'(Z)-alkenyl)-4,5-dihydro-2(3H)-furanones

Chemistry. 2008;14(31):9656-64. doi: 10.1002/chem.200801363.

Abstract

In this paper, it is reported that the efficient iodolactonization of 4,5-allenoic acid with I2 in cyclohexane in the presence or absence of K2CO3 afforded 5-(1'-iodo-1'(Z)-alkenyl)-4,5-dihydro-2(3H)-furanones highly stereoselectively. However, the reaction of axially optically active 4,5-allenoic acids (R)-(-)-5 a and (R)-(-)-5 b with I2 afforded the corresponding products with a serious loss of chirality. This problem was solved by conducting the iodolactonization with N-iodosuccinimide in CH2Cl2 in the presence of Cs2CO3; however, the Z/E selectivity is somewhat lower. The pure optically active Z products were prepared by subsequent kinetic resolution with Sonogashira coupling. The reaction of the substrates with a substituent at the 3-position of the starting 4,5-allenoic acids afforded the trans-4,5-disubstituted gamma-butyrolactones as the only products. The reaction of the 4,5-allenoic acids (S)-(+)-1 l, (R)-(-)-1 l, and (S)-(+)-1 m with a center chirality at the 3-position afforded the trans products with very high enantiopurity and up to 98:2 Z/E selectivity regardless of the axial chirality of the allene moiety.

MeSH terms

  • Alkenes / chemistry*
  • Furans / chemical synthesis*
  • Furans / chemistry
  • Hydrogen / chemistry*
  • Imidazoles / chemistry*
  • Indoles / chemistry*
  • Kinetics
  • Lactones / chemistry*
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Molecular Structure
  • Stereoisomerism

Substances

  • Alkenes
  • Furans
  • Imidazoles
  • Indoles
  • Lactones
  • S-(2-carboxy-1-(1H-imidazol-4-yl)-ethyl)-3-thiolactic acid
  • Hydrogen