NMR spectroscopic investigations of mixed aggregates underlying highly enantioselective 1,2-additions of lithium cyclopropylacetylide to quinazolinones

J Am Chem Soc. 2001 Sep 19;123(37):9135-43. doi: 10.1021/ja0105616.

Abstract

The solution structures of mixed aggregates derived from lithium alkoxides and lithium acetylides were investigated as part of a program to develop practical syntheses of quinazolinone-based nonnucleoside reverse transcriptase inhibitors. Low-temperature (6)Li, (13)C, and (15)N NMR spectroscopies reveal that mixtures of lithium cyclopropylacetylide (RCCLi), a (+)-carene-derived amino alkoxide (ROLi), and lithium hexamethyldisilazide (LiHMDS) in THF/pentane afford a (RCCLi)(3)(ROLi) mixed tetramer, a C(2)-symmetric and asymmetric (RCCLi)(2)(ROLi)(2) mixed tetramer, and a C(3)-symmetric (RCCLi)(ROLi)(3) mixed tetramer. Analogous mixtures of RCCLi/ROLi in Et(2)O and Me(2)NEt also provide 3:1, 2:2, and 1:3 mixed tetramers. The stereochemistry of aggregation is highly sensitive to the medium. The C(2)-symmetric (RCCLi)(2)(ROLi)(2) mixed tetramer is formed in Et(2)O, whereas the asymmetric isomer is formed in Me(2)NEt. LiHMDS in THF is shown to be an efficient proton scavenger without forming LiHMDS-RCCLi or LiHMDS-ROLi mixed aggregates. LiHMDS-RCCLi mixtures form mixed aggregates in Me(2)NEt.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Furans
  • Lithium / chemistry*
  • Magnetic Resonance Spectroscopy / methods
  • Quinazolines / chemical synthesis*
  • Quinazolines / chemistry
  • Reverse Transcriptase Inhibitors / chemical synthesis*
  • Reverse Transcriptase Inhibitors / chemistry
  • Stereoisomerism

Substances

  • Furans
  • Quinazolines
  • Reverse Transcriptase Inhibitors
  • tetrahydrofuran
  • Lithium