Preparation of α-substituted γ-alkoxyallylstannanes from β-tributylstannyl acrolein acetals: scope of the method and primary rationalization of the obtained results

2-C-Alkynyl and 2-C-cis-Alkenyl β-Mannosides with Acetal Protected γ-Aldehyde Functionality via 2-Uloside Alkynylation and Lindlar Hydrogenation

“…The carbohydrate system was found to comprise a distorted 4 C1 conformation. Subsequently, alkynylation of 2 with propiolaldehyde dibenzyl acetal [9] and n-butyllithium gave 2-C-alkynyl mannoside 3a in 85% yield. The attack of the nucleophile solely occurred from the equatorial side and no diastereomeric byproduct could be detected.…”

“…Dess-Martin periodinane was prepared via the potassium bromate method [22]. Propiolaldehyde dibenzyl acetal was prepared according to the method published by Fliegel et al [9]. The following reagents were commercially available and used without further purification: Lindlar catalyst, para-toluenesulfonic acid, acetic anhydride, 4-(dimethylamino)pyridine (Sigma-Aldrich Chemie, Munich, Germany), 1,3-dihydroxypropane (abcr, Karlsruhe, Germany), n-butyllithium (Fisher Scientific, Nidderrau, Germany), triethylamine (Th.…”

“…Propiolaldehyde dibenzyl acetal [9] (1.02 g; 4.04 mmol) was dissolved in anhydrous THF (35 mL) and cooled to −80 • C. n-Butyllithium (1.50 mL; 4.04 mmol; 2.7 M in n-heptane) was added dropwise and stirring at −80 • C was continued for 2.5 h. Next, 2-uloside 2 (1.98 g; 3.67 mmol) in 30 mL THF was added dropwise over 15 min. After stirring for another 15 min, the reaction was quenched by the addition of satd.…”

Synthesis, characterization and primary evaluation of the synthetic efficiency of supported vinyltins and allyltins

“…In the tributyltin series, a-substituted c-alkoxyallyltins were obtained from acrolein b-tributylstannylacetals through a S N 2 0 reaction [29,30]; therefore, a similar reaction for the supported analogues 5b-E and 5b-Z according to Scheme 8, was expected, see Table 5.…”

“…In practice, using tributyltin reagents [29,30] for the synthesis of supported allyltins appears to be much less efficient. For instance, using MeCu(CN)Li and LiBr in diethyl ether or THF, the S N 2 0 reaction product 11a could not be obtained, whatever the reaction conditions.…”