Total synthesis of (+)-blastmycinone, (-)-litsenolide C-1, and related natural trisubstituted lactones via alkynyltungsten compounds

A general method for total synthesis of natural trisubstituted gamma-lacton es is developed on the basis of the chemistry of alkynyltungsten compounds. The key step in this approach involves the cycloalkenation of tungsten-eta (1)-(3R,4S)-pent-1-yne-3,4-diol with aldehydes to give;tungsten-oxacarbeniu m salts, further leading to 3-alkylidene-4-hydroxy-5-methyl-gamma-lacton up on demetalation. This synthetic sequence proceeds well for alkynylaldehydes and the MOM derivative of tungsten-eta(1)-(3R,4S)-pent-1-yne-3,4-diol. The resulting butyrolactone products are transformed into natural trisubstitut ed butyrolactones including (+)-blastmycinone, (+)-blastmycinolactol, (+)an timycinone, NFX-2, and (+)-isodihydromahubanolide A. By using the same appr oach based on (R)-ethyl lactate, the natural (-)-litsenolide C-1 can be pre pared in a few steps.