THE CHEMISTRY OF METALLACYCLIC ALKENYLCARBENE COMPLEXES .6. REGIOSELECTIVE SYNTHESIS OF SUBSTITUTED (3E)-1,3-DIENES FROM CHELATED ALLYL-IRONCARBENE COMPLEXES AND POTASSIUM ENOXYBORATES

The addition of potassium enoxyborates to the chelated allyl-iron-carb ene complex 1 leads to the corresponding eta(4)-(3E)-1,3-diene complex es 2 in fair yields. Complexes 2 can be demetalated with eerie ammoniu m nitrate (CAN) to give unrearranged (3E)-6-oxo-1,3-dienes 3. Prior to decomplexation, the carbonyl group can be further modified. This is d emonstrated by the syntheses of the natural terpene alcohol hotrienol and of a complexed methylene-separated dienyne. Potassium enoxyborates are superior to lithium enolates as they are readily prepared in situ from a variety of al dehydes and ketones which do not form sufficient ly stable lithium derivatives. In contrast to lithium enolates, only C -C coupling products derived from the ''kinetic'' regioisomers are for med from unsymmetrical aliphatic ketones.