Y- -alkylidene butenolides

Following the same principle Fiandanese and coworkers [111] have developed an efficient stereoselective approach to silylated polyunsaturated y-alkylidene butenolides 143-145 starting from Z-3-iodo-propenoic acid (Scheme 55). 

Scheme 55 Polyunsaturated y-alkylidene butenolides by sequential Sonogashira coupling-cyclization [111] (newly formed bonds drawn in bold lines)...

Finally, it was reported that dianions derived from dicarbonyl compounds react in a straightforward manner with dielectrophiles derived from oxalic acids, yielding interesting y-alkylidene butenolides or their aza counterparts. However, hydrolysis conditions are critical in the case of the aza derivatives600,601. 

The reaction of thyinoquinone (74) to yield the y-alkylidene-A -butenolide (79) illustrates the interesting chemistry that 1,4-quinones exhibit upon reaction with sodium azide in trichloroacetic acid . Intermediates 75, 76 and 78 were synthesized and shown to... 

It was shown that for a variety of substituents the y-alkylidene-(or arylidene)-A -butenolides (84) could be obtained in good yields (60-90%, mostly over 80%) It has been pointed out that the... 

Heck reaction. The coupling of iodc the normal /3-aminomethylstyrenes (in Et( In the presence of CuI-Et.,N the Pd-cau thesis of y-(Z)-alkylidene butenolides fro pling of l-penten-4-yn-3-ol with Arl occu An interesting chemoselectivity is shot flates as a result of slight structural varia... 

Ishikawa, T. Nishigaya, K. Uchikoshi, H. Chen, I-S. Cochinolide, a New y-Alkylidene Bicyclic Butenolide with Antiviral Activity and Its P-Glucopyranoside from Homalium cochinchinensis. J. Nat. Prod. 1998, 61, 534-537. 

A similar synthesis of (Z)-a-alkylidene-y-lactones from alkenyl iodides was reported by Luo et al. In a related procedure,the presence of an acetyl group a to the hydroxyl group of the iodide led to the formation of a,/S-unsaturated butenolides. The presumed intermediate a-methylene lactone probably undergoes isomerization to the more stable butenolide under the reaction conditions, as shown in Scheme 8. 

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