http://revach.net/article.php?id=1227

Section: Halacha   Category: Tshuvos
Rav Shlomo Zalman Auerbach: Reciting VaYechulu During Elokai Netzor

If a person has not yet completed his Shmoneh Esrei and he is up to Elokai Netzor, and the tzibbur is reciting VaYechuhlu, is it permissible to recite the VaYechulu with them? R. Shlomo Zalman Auerbach rules that it is permissible to do so if he has already recited ‘Yihiyu LeRatzon'. Even though only certain things are permitted to be recited during Elokai Netzor, such as ‘Yehei Shmei Rabah', however VaYechulu is an exception because it is part of the Friday night Shmoneh Esrei. Since it is recited during the Shmoneh Esrei it is permissible to recite it again in middle of Eloka'i Netzor. (Sefer Me'or ha'Shabbos)

Disclaimer: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.