Influence of Michael acceptor stereochemistry on intramolecular Morita-Baylis-Hillman reactions

[reaction: see text] A study of the effect of Michael acceptor stereochemistry on the efficiency of intramolecular Morita-Baylis-Hillman (MBH) reactions has been performed. The reactions were catalyzed by a phosphine, and the reaction substrates studied were enones containing a pendant aldehyde moiety attached at the beta-position of the alkene group. In all cases examined with PPh3 as the catalyst, cyclization substrates possessing (Z)-alkene stereochemistry afforded a much higher yield of the desired product than did the E isomeric substrates under identical reaction conditions. This was also true when a polymer-supported phosphine catalyst was used. While both alkene isomers afforded the same product, in parallel reactions, the Z isomer afforded 2.5-8.5 times higher yield than did the corresponding E isomer. It is proposed that steric effects are a possible source of this dramatic difference in reactivity. Substrates where the beta-substituent is cis to the electron-withdrawing substituent are relatively more accessible to react with the nucleophile catalyst than are their trans counterparts. These findings are expected to be useful in the design of synthetic intermediates, as intramolecular MBH reactions are being increasingly used in the preparation of complex synthetic targets.     

纸质活性炭纤维的制备及性能表征

通过KOH活化纸巾制备活性炭纤维, 比表面积高达1388 m²/g. 用制得的活性炭纤维作为吸附剂进行亚甲基蓝吸附实验研究,用Langmuir和Freundlich吸附模型分析实验数据,并研究pH值对活性炭纤维吸附亚甲基蓝影响. 活性炭纤维吸附速率更适于Pseudo-second-order动力学模型,相关系数高达0.998. 整个浓度变化区间Langmuir吸附等温线比Freundlich吸附等温线更适合实验数据. 所制备活性炭纤维对亚甲基蓝最大平衡吸附量为520 mg/g,实验发现,pH值越高活性炭纤维对亚甲基蓝吸附量越大.     

Transverse optical patterns for ultra‐low‐light‐level all‐optical switching

We review recent theoretical and experimental efforts toward developing an all‐optical switch based on transverse optical patterns. Transverse optical patterns are formed when counterpropagating laser beams interact with a nonlinear medium. A perturbation, in the form of a weak switch beam injected into the nonlinear medium, controls the orientation of the generated patterns. Each state of the pattern orientation is associated with a state of the switch. That is, information is stored in the orientation state. A realization of this switch using a warm rubidium vapor shows that it can be actuated by as few as 600 ± 40 photons with a response time of 5 µs. Models of nonlinear optical interactions in semiconductor quantum wells and microresonators suggest these systems are also suitable for use as fast all‐optical switches using this same conceptual design, albeit at higher switching powers.