Lithiated 1,3-dicarbamates

In the lithiated dicarbamate 111 of (S)-2-(dibenzylamino)-l,4-butanediol (derived from L-aspartic acid) the 4-carbamoyloxy group also possesses a high tendency for intramolecular complexation [Eq. (31)] [75, 76]. The favorable equatorial positions of the dibenzylamino and 1-carbamate groups are displayed in the transition state of the deprotonation. When treated with sec-butyl-lithium in ether or THE, the bicyclic chelate complex 111 is formed exclusively by removal of the pro-S-IH atom. Trapping of 111 by many types of electrophiles gives stereohomogeneous substitution products 112 [Eq. (31), Table 3]. Since deprotection proceeds easily by the usual means, anion 111 constitutes a synthetic equivalent of the synthon 114. No deprotonation in the 4-position was detected, however this can be achieved by protecting the pro-S-lH by conversion to deuterium (see below and Sect. 2.5). 

Guamieri, W. Sendzik, M. Frohlich, R. Hoppe, D. Regio- and stereoselective lithiation and C-substitution of (S)-2-(dibenzylamino)bu-tane-l,4-diol via dicarbamates. Synthesis 1998, 1274-1286. 

The dicarbamates 254 were smoothly lithiated by using f-BuLi—TMEDA at —80°C and then allowed to warm to room temperature over 16 hours. Under these conditions a smooth anionic ortfio-Fries rearrangement gave the diamido derivatives 255 in fair yields (25-80%) (equation 117) (see also Reference 220). A similar rearrangement was also described for [2,2]-paracyclophanes. ... 

The 1,3-dicarbamate 19 undergoes a stereoselective cyclopropanation after lithiation with s BuLi (-)-3. Depending on the nature... 

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