Alkenyl Anions and Synthetic Equivalents

New acyl anion equivalents have proved to be popular targets for research and this year is no exception. For example anion (37) reacts with aldehydes (R CHO) to give acrylates (38), and amidrazones (39) provide access to the acyl anion equivalents (40). The latter undergo electrophilic attack to yield ketones [RCH2C(0)E] after unmasking. Similarly, 1,4-diketones are obtained from the addition products of acyl anion equivalent (41) and a,/3-unsaturated ketones. Cyclic a,/3-unsaturated ketones (42) are in turn formed by addition of the /S-acyl anion equivalent (43) to electrophiles. The 5-oxocyclopentenyl equivalent (44, X = Li) is generated in three steps from the cyclopentenone 

Seuron, L. Wartski, and J. Seyden-Penne, Tetrahedron Lett., 1981, 22, 2175. 

Aldehydes (RCHO) react with 1-diazo-l-lithioacetone to give a-diazo- -hydroxyketones (48). These latter compounds can then be converted to P-diketones by the addition of rhodium(il) acetate a procedure which has been applied in the synthesis of -damascone. 1,6,6A -Trithiapentalene and a metal salt catalyse the lithiation of unactivated alkenes to alkenyl-lithiums by lithium metal, constituting a very useful method for preparing such compounds since in the past the preparation of alkenyl-lithiums from lithium metal has been confined to alkenes containing relatively acidic protons. Finally, the allenyl-lithium reagent (49) can be converted to various functionalized allenes by simple electrophiles.  

Miscellaneous.—Several useful lithium-based synthetic procedures have been reported this year which involve the preparation or further functionalization of carbonyl compounds. For example aldehydes can be prepared by reaction of an organolithium, RLi, with the formylpiperidine (50). Unsymmetrically 

A new carboxylic ester synthesis involves the addition of lithium dialkyl-cuprates to 5-2-pyridylthioates in the presence of oxygen, whereas in its absence very good yields of ketones are obtained. Additionally, ketones (52) react with 2-lithioesters (53) to give a, -unsaturated esters (54), which can be elaborated to A -butenolides by acidification and reduction.  

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