The first uncatalyzed, diastereoselective vinylogous Mukaiyama aldol reaction is reported, between pyrrole/furan-based dienoxy silanes and aromatic aldehydes on salty water/methanol medium, at almost human body temperature, under ultrasonic irradiation. With pyrrole dienes the reaction is anti-selective, while that of furan dienes is syn-selective. The dual role of water as both reaction medium and promoter is highlighted.