The chemistry of spiroacetals. Preparation of a chiral disubstituted lactone derivative; a key intermediate for synthesis of the spiroacetal moieties of the avermectins and milbemycins

Preparation of chiral lactone from laevoglucosan; a key intermediate for synthesis of the spiroacetal moieties of the avermectins and milbemycins

“…3~ aqueous potassium hydroxide (11) was heated at gentle reflux for 9 h. The dark solution was cooled to room temperature and neutralised with 10% aqueous sulphuric acid. The water was then evaporated under reduced pressure (10 mmHg) to yield a brown semisolid.…”

The chemistry of spiroacetals. Enantiospecific synthesis of the spiroacetal units of avermectins B1b and B2b

“…Proton He (6 3.96) shows the characteristic deshielding due to the 173-diaxial interaction with the oxygen of the adjacent ring. 1 Elaboration of (1) to the spiroacetal unit of avermectin B2b was achieved by a simple two step sequence (Scheme 4).…”

Stereoselective Synthesis of Fully Protected (S)‐1,7‐Dioxaspiro[5,5]undec‐4‐ene Derivatives of Sugars

“…[2,3] Indeed, the (S) stereochemistry at the spirocentre represents an interesting synthetic outcome inasmuch as such a configuration is that shown by a wide group of natural products [4,5] containing a symmetrically disposed 1,7-dioxaspiro [5,5]undecene spiroacetal motif. Specifically, the calcium-binding ionophore [6] A 23187 and the group of potent anthelmintic antibiotics comprising the avermectins [7] and milbemycins [8] offer awe-inspiring examples of such structures. For these reasons we considered modifying our former synthetic approach in order to devise a new and reliable method for the preparation of 1,7-dioxaspiro [5,5]undec-4-ene derivatives of sugars, in which we are interested to perform a new synthesis of avermectin B 1a .…”