Total synthesis and repudiation of the helianane family.

Organic letters (2011-09-21)
Jason C Green, Sandra Jiménez-Alonso, Eric R Brown, Thomas R R Pettus
ABSTRACT

Total syntheses of two structures purported as (+)-heliananes were completed in six pots. Spectral comparisons, between the synthetic and natural compounds, revealed a misassignment of the eight-membered ring in the heliananes. The key step in the syntheses of the proposed structures and the confirmation of their actual structures was a diastereoselective inverse-demand Diels-Alder reaction between an optically active enol ether and an ortho-quinone methide species, which was generated in situ at low temperature by the sequential addition of methylmagnesium bromide and di-tert-butyl dicarbonate to a salicylaldehyde.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Di-tert-butyl dicarbonate, ReagentPlus®, 99%
Sigma-Aldrich
Di-tert-butyl dicarbonate, ≥98.0% (GC)
Sigma-Aldrich
Di-tert-butyl dicarbonate, ReagentPlus®, ≥99%
Sigma-Aldrich
Isopropyltriphenylphosphonium iodide, 98%
Sigma-Aldrich
Di-tert-butyl dicarbonate solution, 1.0 M in THF
Sigma-Aldrich
Di-tert-butyl dicarbonate solution, 2 M in methylene chloride
Sigma-Aldrich
Di-tert-butyl dicarbonate solution, 2 M in THF