Asymmetric reactions in continuous flow

• Xiao Yin Mak,
• Paola Laurino and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2009, 5, No. 19, doi:10.3762/bjoc.5.19

• was developed for the reaction of imino esters with ketenes, leading to the stereoselective synthesis of ß-lactams [30]. Ketene was generated from the corresponding acid chloride with polymer-supported BEMP 17, and was reacted with an imino ester in a reaction catalyzed by the resin-supported quinine

• derivative 18. In this way, the handling and isolation of reactive ketene intermediates was directly avoided. A long and rigid linker to the resin was found to be ideal for obtaining good selectivities in this reaction. Nucleophilic scavenger 19 was used to remove excess reagents and byproducts. This three

Catalytic synthesis of (E)-α,β-unsaturated esters from aldehydes and 1,1-diethoxyethylene

• Rubén Manzano,
• Lidia Ozores,
• Andreas Job,
• Lars Rodefeld and
• Benjamin List

Beilstein J. Org. Chem. 2009, 5, No. 3, doi:10.3762/bjoc.5.3

• leads to the formation of water and CO2 as the only by-products (Scheme 1, eq 3) [23][24]. Here we describe as a new approach, the boronic acid-catalyzed condensation of ketene dialkyl acetal with aldehydes to furnish α,β-unsaturated esters in good yields and reliably high (E)-stereoselectivities

• (Scheme 1, eq 4). Although previously attempted under thermal conditions with poor success, our catalytic reaction is entirely new [25]. We reasoned that the reaction of readily available and inexpensive ketene diethyl acetal [26] or ketene dimethyl acetal (available from Aldrich) with aldehydes upon

• treatment with a suitable reagent or catalyst could readily lead to the corresponding unsaturated ester and ethanol or methanol as the only by-product. The use of ketene dialkyl acetals for organic transformations is infrequent [27]. To the best of our knowledge, they have been employed in [2+2

Aroylketene dithioacetal chemistry: facile synthesis of 4-aroyl- 3-methylsulfanyl- 2-tosylpyrroles from aroylketene dithioacetals and TosMIC

• H. Surya Prakash Rao and
• S. Sivakumar

Beilstein J. Org. Chem. 2007, 3, No. 31, doi:10.1186/1860-5397-3-31

• heterocyclic systems, examples of their participation in the cycloaddition reactions are rare. In continuation of our interest on ketene acetals [5][6][7] we considered that 1,3-dipolar cycloaddition of the anion generated from the von Leusen's reagent (p-tolylsulfonyl)methyl isocyanide (TosMIC) 2 to AKDTAs 1

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

• 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

• reaction, in line with our expectations, exemplified by the reactions of cyclohexyl-substituted ketene 1d (entries 7 and 8, compared with entries 1–6). In almost all cases, if reactions were left for extended periods beyond consumption of starting material, small quantities of desilylated allenes were

• silylketenes with reactive ylides involves deprotonation by the basic reagent to generate ynolate anions. Clearly, since such a pathway cannot operate with the substituted ketenes used here other mechanisms are at play, which may include nucleophilic desilylation or ketene oligomerisation initiated by