Wittig Reaction, Stereochemistry of Schlosser

Schlosser, M., Christmann, K. F. Olefination with phosphorus ylides. I. Mechanism and stereochemistry of the Wittig reaction. Liebigs Ann. Chem. 1967, 708, 1-35. 

In 1970, a review entitled The Stereochemistry of the Wittig Reaction was published in Topics of Stereochemistry by M. Schlosser (1). This review was a milestone in early attempts to understand the Wittig mechanism based on a stepwise, ionic process (Scheme 1) (1,2). The reaction of ylides with aldehydes was believed to involve a partly reversible nucleophilic addition step to generate a betaine intermediate (1 or 2). Subsequent decomposition to the alkene was attributed to the formation of oxaphosphetanes 3 or 4, structures that were assumed to be intermediates of higher energy leading from the betaine to the alkene. 

Scheme 5.1 depicts a typical representation of the Wittig reaction, which is one of the most commonly used olefin preparation reactions [1]. The reaction was developed by Georg Wittig, who was a Nobel Prize laureate in 1979. The control of dia-stereochemistry in the product has been studied in detail by Schlosser. Both the E and Z diastereomers can be obtained with excellent selectivity by means of Schlosser s modified method [2]. 

In 1966, Schlosser and Christmann, as a way of controlling the stereochemistry of the reaction, published a variation that provided support for the classical mechanism of the Wittig reaction. The Schlosser modification allowed for a /ra 5-selective outcome for the alkene geometry. 

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