[maverick1996]

Hey guy!

When I react a ylid with an aldehyde, the product is an alkene and I just assumed that a trans alkene would be more favourable due to less steric repulsion etc.

But I am doing some questions, the specific question is EtCHO with Ph3P=CHCH2CH2CH3 (sorry about not formatting this properly) and again I assumed the trans alkene is the majority product but the answers say 'EtCH=CHCH2CH2CH3, 90% cis-isomer'

Can somebody help me out and explain why the cis alkene is the majority product?

Thank you

[Alwin Kristen]

Stereoselectivity of Wittig-reaction depends of the ylid. With stabilized ylid (delocalized negative charge) reaction is E (trans) selective and with unstabilized ylid its Z (cis) selective. I have attached a picture from J. Claydens book; Organic Chemistry, to clarify Z selectivity.

[maverick1996]

Stereoselectivity of Wittig-reaction depends of the ylid. With stabilized ylid (delocalized negative charge) reaction is E (trans) selective and with unstabilized ylid its Z (cis) selective. I have attached a picture from J. Claydens book; Organic Chemistry, to clarify Z selectivity.

Thank you