No abstract

Reaction of electrophilic allyl halides with nucleophiles gave rise to competitive substitution-MIRC (Michael initiated ring closure) reactions dependent upon the number of electronwithdrawing groups (Y,Z), the substitution pattern of the activated double bond (R1,R ,R ) and the nature of the nucleophile.2 3Monoactivated allyl halides merely afforded substitution products 2 , 3.However with double activated substrates the sterical crowding around the double bond plays a dominant role. Compounds with R =H gave rise to MIRC products -6, 1, while in the case of tetrasubstituted alkenes MIRC products are formed with Nu=OR, CN, H and substitution products with Nu=SR, amines. The rate limiting step in the MIRC reaction consists of the Michael addition followed by a fast cyclization when R3=H.closure for compounds with R3=Me.can be interpretated by the role played by the pKa difference between the conjugate acids of the nucleophile and the carbanion upon the position of the overall equilibrium. 3On the contrary the rate limiting step is the ringThe competitive substitution-MIRC reaction -430 -

Die Selbstkondensation von Chloraceton (I) in Gegenwart von TiCl4 in Pyridin zum Dichlormethylpentenon (II) erfolgt bereits bei Raumtemperatur.

A new explanation for the apparant contradiction in the Hofmann and Saytzeff‐rules in elimination reactions is advanced. Evidence is given to show that Hofmann elimination occurs as the consequence of an irreversible reaction. Eliminations following the Saytzeff rule then are reversible reactions, giving the most stable products.

Die Reduktion der β‐Halogenethylidenmalonsäurediester (I) mit LiAlH4 liefert die Bis‐hydroxymethylcyclopropane (II) in guten Ausbeuten.