Synthesis of highly substituted allenylsilanes by alkylidenation of silylketenes

• Stephen P. Marsden and
• Pascal C. Ducept

Beilstein J. Org. Chem. 2005, 1, No. 5, doi:10.1186/1860-5397-1-5

• )ketenes were used as substrates.[16][17] Thus, only 3-substituted and 3,3-disubstituted allenylsilanes have thus far been accessed by alkylidenation of silylketenes, whilst no reports of the successful introduction of non-stabilised ylide equivalents have been forthcoming. A second impediment to the

• yield, Scheme 2, Table 2. As expected, reactions with the more substituted ylide 4 were significantly slower than those with the parent ylide 5 (compare reaction temperatures and times, entries 1, 3 and 5 versus entries 2, 4 and 6). Increasing the steric bulk of the ketene substituent also slows the

Reagent controlled addition of chiral sulfur ylides to chiral aldehydes

• Varinder K. Aggarwal and
• Jie Bi

Beilstein J. Org. Chem. 2005, 1, No. 4, doi:10.1186/1860-5397-1-4

• transformations.[1] Indeed, near perfect levels of asymmetric induction with high diastereocontrol have been achieved with aromatic aldehydes (Scheme 1). In such reactions, the C1 stereochemistry is controlled by ylide conformation, face selectivity, and the degree of reversibility in formation of the anti

• clearly shown by sulfide 2 could be exploited in reactions with chiral aldehydes and to what extent it might dominate over substrate control (Scheme 2).[3] Again C1 stereochemistry should be controlled by ylide conformation, face selectivity, degree of reversibility in anti betaine formation, and is not

• (dimethylamino)-phosphoranylidene]-phosphoric triamide ethylimine,) [4][5] (sulfur ylide 4) was initially investigated to establish the degree of substrate control. This furnished a mixture of 3 epoxides 7a, 7b, and 7c in a 37:14:49 ratio (Table 1, entry 1). The cis and trans isomers are easily distinguished by