Lewis Acid Activated Reactions of Mixed (O,Se) Acetals with Allyltrimethylsilane and Allyltributylstannane
摘要:
On the basis of preferential complexation of oxygen or selenium atoms by different Lewis acids, it was expected that, depending on the Lewis acid employed, the title reactions would lead to selective formation of homoallyl ethers or homoallyl selenides. This has not been confirmed by experiment: in almost all the reactions tried homoallyl ethers largely predominated; or were the exclusive allylation products, even when strongly oxygenophilic Lewis acids such as TiCl4 were used. In the cases of the latter type of Lewis acids, the results observed with (O,Se) and a couple of(O,S) mixed acetals are-interpreted in terms of two major factors operating in opposite directions. H-1 NMR data of a mixture of TiCl4 and (O,Se) acetal indicate that preferential (but not exclusive) complexation of the oxygen moiety takes place indeed. However, because of the much stronger C-O bond as compared to the C-Se bond, this latter.(also activated by the Lewis acid to some extent) undergoes cleavage by allyl metals to give homoallyl ethers as predominating products. In contrast with BF3 . OEt(2), boron trichloride and boron tribromide were found to react with (O,Se) acetals to give the corresponding alpha-halo selenides, which in turn were cleanly transformed into homoallyl selenides on reaction with allyltrimethylsilane in the presence of tin tetrachloride.
Indirect Cation Pool Method. Rapid Generation of Alkoxycarbenium Ion Pools from Thioacetals
作者:Seiji Suga、Kouichi Matsumoto、Koji Ueoka、Jun-ichi Yoshida
DOI:10.1021/ja0625778
日期:2006.6.1
the electrochemical generation and accumulation of ArS(ArSSAr)+ at low temperature (step 1) and the follow-up reaction with a thioacetal to generate an alkoxycarbeniumion pool (step 2), which reacts with various carbonnucleophiles (step 3). Steps 2 and 3 are extremely fast. The electrogenerated ArS(ArSSAr)+ was well-characterized by 1H NMR and CSI-MS. The alkoxycarbeniumion pool generated by the
Direct and indirect electrochemical generation of alkoxycarbenium ion pools from thioacetals
作者:Kouichi Matsumoto、Koji Ueoka、Shinkiti Suzuki、Seiji Suga、Jun-ichi Yoshida
DOI:10.1016/j.tet.2009.09.020
日期:2009.12
Thioacetals were found to be effective precursors to generate and accumulate alkoxycarbeniumions based on direct and indirect cation pool methods. Alkoxycarbeniumions thus generated reacted with carbonnucleophiles such as allylsilanes and enol silyl ethers to give C–C bond formation products in good yields.
Lithium Bromide, a Novel and Highly Effective Catalyst for Monothioacetalization of Acetals under Mild Reaction Conditions
作者:Fumiaki Ono、Ryojyu Negoro、Tsuneo Sato
DOI:10.1055/s-2001-17477
日期:——
Lithium bromide is efficient as a catalyst for the monothioacetalization of acetals under mild reaction conditions to provide products in excellent yields with high chemoselectivity.
Indirect Cation-Flow Method: Flash Generation of Alkoxycarbenium Ions and Studies on the Stability of Glycosyl Cations
作者:Kodai Saito、Koji Ueoka、Kouichi Matsumoto、Seiji Suga、Toshiki Nokami、Jun-ichi Yoshida
DOI:10.1002/anie.201100854
日期:2011.5.23
Go with the flow: The indirect cation‐flow method based on the generation of highly reactive organic cations from their precursors using electrochemically generated [ArS(ArSSAr)]+ was developed in flow microreactor systems (see scheme; Bn=benzyl, M=micromixer, R=microtube reactor). The method was applied to evaluate glycosyl cations such as A or their equivalents and glycosylation reactions.
Monothioacetals are obtained by treating the corresponding acetals with organotin thiophenoxides in the presence of BF2·OEt2. The reaction proceeds under mild conditions to provide the desired compounds with high selectivity.