P-alkoxyacrylates

Boron tnchlonde acting as a Lewis acid cleaves ben/ylic ether 37 selectively to 38.IJ The third reaction, like the transiormation of 4 to 5, leads to a rranv-P-alkoxyacrylate 7... 

The intramolecular Michael addition reaction of ketone enolate to p-alkoxyacrylate proceeded selectively (in a ratio of 5.9 1) with Barton s base (5) to give tetrahydrofuran 36 [8]. In a model smdy, LDA was much less effective than Barton s base (28 5% versus 96% yield). The diester 36 was converted into 38, which corresponds to the A-D ring system for lactonamycin (39) (Scheme 7.6). 

Pyrans result from the intramolecular capture of radicals derived from P-alkoxyacrylates. The 3-hydroxy function in the product allows a reiterative approach, providing a route to fused bipyians (94TL129). 

Under oxidative conditions, acyclic [75a,b] and cyclic [75c] 4-yn-l-ols react via a cyclization-methoxycarbonylation pathway to afford ( )-cyclic-P-alkoxyacrylates 2E-[(methoxycarbonyl)methylene]tetrahydrofurans in good yields under mild conditions (Equations 10.37 and 10.38). The stereochemical outcome is entirely consistent with a reaction initiated by intramolecular nucleophilic attack of the hydroxy group on the palladium-coordinated triple bond to generate a vinylpalladiumiodide intermediate that undergoes methoxycarbonylation to afford the P-alkoxyacrylate. The ketopyranose subunit can also be constructed via a palladium-catalyzed oxidative cyclocarbonylation of substituted 5-yn-l-ols, which occurs with excellent stereose-... 

However, following the methodology developed by Kato and Akita, a great variety of P-alkoxyacrylates have been synthesized starting from 4-yn-l-ols [95], cyclic 2-propargyl-l-ols [96], or 2-propargyl-l-ones [97-99] (Scheme 13.52). 

Kato, K., Nishimura, A., Yamamoto, Y. and Akita, H. (2001) Improved method for the synthesis of (E)-cyclic-P-alkoxyacrylates under mild conditions. Tetrahedron Letters,... 

---