Diastereoselective synthesis of chiral α-aminoorganotributyltins via ring-opening of 2-tributylstannyloxazolidines

Stereoselective Synthesis of Stannylated Dehydropiperidines and Dehydroazepanes

“…Furthermore, these assignments were corroborated by NOESY experiments. The diastereoselectivity of the synthesis of 2‐tributylstannyl‐1,3‐oxazolidines was already rationalized when using ( R )‐phenylglycinol,[7b], and in the present case, the reaction mechanism does not allow a very strong preference for one diastereoisomer regardless of the nature of the protecting group or the presence of a phenyl group on the double bond (styryl series). This is due to a lack of differentiation between the two possible transition states and also to the possible cis/trans isomerization of the 2‐tributylstannyl‐1,3‐oxazolidines via iminium ion generation in the presence of BF 3 · OEt 2 .…”

“…Products trans and cis 2‐tributylstannyl‐1,3‐oxazolidines 3 were obtained in moderate to good yields [Table , Entries 1–5 (45–79 %)] and comparable to those obtained with ( R )‐phenylglycinol. [7a] Interestingly, yields were found to be higher when reactions were carried out in benzene instead of cyclohexane which is most likely due to the higher solubility of N ‐protected β‐amino alcohols 2 in such solvent (65 % compared to 45 % for 3a , Table , Entries 1 and 2; and 79 % compared to 61 % for 3c , Table , Entries 4 and 5). The assignment of the trans or cis configuration was unambiguously obtained on the basis of 3 J Sn‐C‐Z‐C , 3 J H‐H , 2 J Sn‐H and δ H2 values for the oxazolidine NMR spectra; these agreed well with our previous work and with theoretical studies reported for the evaluation of 3 J Sn‐C‐Z‐C .…”

“…Taking advantage of our knowledge in this domain we carried out reactions using allyltributyltin or higher order lithium butenylcyanocuprate in order to obtain our key dienyl intermediates 4 and 5 , precursors of the desired stannylated dehydropiperidine/azepane species. This reaction requires Lewis acid assistance and BF 3 · OEt 2 was found to provide the best results; stronger Lewis acids were found to induce the transmetalation of 3 . For this purpose, we have primarily considered ( S )‐vinylglycinol derivatives as reported in Table .…”

“…We have reported an efficient ring‐opening reaction of 2‐tributylstannyl‐1,3‐oxazolidines derived from ( R ) or ( S )‐phenylglycinol that generates enantioenriched α‐stannylated N ‐protected β‐amino alcohols . When the nitrogen was protected as a carbamate and the oxygen protected as an O ‐silyl ether, the Sn/Li transmetalation reaction of these derivatives and subsequent electrophilic trapping was shown to proceed stereospecifically with retention of configuration , .…”

Copper(I) Iodide

“…17 This reaction proceeds in a diastereoselective fashion in favour of the anti isomer (dr close to 85:15).…”