STEREOSELECTIVE SYNTHESIS OF 2,5-DIHYDROFURANS BY SEQUENTIAL SN2' CLEAVAGE OF ALKYNYLOXIRANES AND AG-CATALYZED CYCLIZATION OF THE ALLENYLCARBINOL PRODUCTS()

The alkynyloxiranes 5a,b, 7, and 18 afford mainly the anti S(N)2' prod ucts 6a,b, 8, and 19a upon treatment with Me2CuLi. The derived primary alcohol silyl ethers 9a,b, 10, and 19b-d undergo Ag+-catalyzed cycliz ation to the 2,5-dihydrofurans 11a,b, 12, and 20b-d. Diol 26 affords m ainly the fused ring 2,5-dihydrofuran 32 under these conditions. The s tereochemistry of dihydrofuran 20a was confirmed by conversion to the known epoxide 21a.