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Aus der propaedeutischen Klinik in Prag. Ueber das Verhalten des Venenpulses bei den durch Extrasystolen verursachten Unregelm~issigkeiten des menschlichen Herzens.

Hexalkylditin is prepared by a Lewis acid-promoted (MgCI 2) reductive reaction of bisurialkyltin) oxide using magnesium metal as reducing agent. Hexabutyl-and hexaphenylditin are synthesized with 95% and 80% yield separately and a radical mechanism is proposed for the reaction condition. Unsymmetric ditin, BuJSn-SnPh J • was first synthesized by this reductive method.tion of Mg and BU3SnCI in dry THF was sonicated for 30 minutes. BuJSn-SnBu, was created as the only product, and the highest yield achieved was 40% even at prolonged reaction time. We also observed that hexabutyldiitin can not be generated from bis(tributyltin) oxide under this ultrasonic condition. Interestingly. hexabutylditin can be afforded from bia(tributyltin) oxide in the presence of Lewis acid (MgBr2) using magnesium as reducing agent under ultrasound (Scheme I). A solution of Mg. 1.2-dibromoethane and (Bu3Sn)20 was sonicated for 2 hours. and BU3Sn-SnBu3 was produced with 45% yield. It has been proposed that MgBr2 is generated in situ when Mg reacts with 1,2-dibromoethane.We also observed that hexaphenylditin (Ph3Sn-SnPh3) can be generated from bis(triphenyltin) oxide with Lewis acid under this sonochemical reaction condition. It should be noted that the tetraphenyltin (PluSn) was not formed as unexpected product observed previously under this reaction condition. Therefore, we are interested in the investigations of these reductive reactions of bis(trialkyltin) oxides with different Lewis acids under ultrasound. A solution of (Bu3Sn)ZO(1.0 eq.), Mg (1.2 eq) and Lewis acid (1.1 eq) in anhydrous THF was sonicated for one hour, and the reductive results are shown in Table I. The results showed that in situ generated MgBr2 is less effective than the added MgBr2 (powder). Other Lewis acids such as MgCb and ZnCh can not promote the reductive reaction under sonochemical reaction conditions. Bis(tributyltin) oxide is resistent to magnesium as reducing agent in the absence of Lewis acid under R =Bu, Ph R 3SnCI or R 3Sn-a-SnR3