Observation of intermediates in Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton containing Group 15 elements with benzaldehyde

Abstract

The heteroatom effect of Group 15 elements (P, As, Sb and Bi) has been investigated on stereochemical drift in the Wittig reactions of non-stabilized phosphonium ylides bearing a phosphaheteratriptycene skeleton with benzaldehyde. 1,2-Oxaphosphetanes were observed as intermediates and the isomerization from cis-form to trans-form, the origin of stereochemical drift, was detected between −90 °C and 25 °C by VT-³¹P{¹H} NMR spectroscopy. The isomerization was found to start at lower temperatures as the raw number of heavier period elements. Cross experiments showed that the isomerization occurred through equilibrium between 1,2-oxaphosphetanes and phosphonium ylides-benzaldehyde.GRAPHICAL ABSTRACT

Keywords:

• Heteroatom effect
• 1,2-Oxaphosphetane
• stereochemical drift
• isomerization
• phosphaheteratriptycene skeleton

Disclosure statement

No potential conflict of interest was reported by the authors.

Acknowledgements and thanks

This study was partially supported by a Grant-in-Aid for Encouragement of Young Scientists (B) to Y. U. (No.16750041 and No.18750037) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan and Kitasato University Research Grant for Young Researchers. The authors thank Emeritus Prof. Takayuki Kawashima for useful advices.