Highly diastereoselective addition of allyltitanocenes to ketones.
A route with less congestion: A practical method for the highly diastereoselective preparation of anti tertiary homoallylic alcohols has been developed. The reaction of allyltitanocenes, generated by the reductive titanation of various allylic substrates with a titanocene(II) species, with a variety of ketones produced the anti tertiary homoallylic alcohols in good diastereoselectivity, even when using sterically less congested ketones (see scheme; Cp: cyclopentadienyl; Piv: pivaloyl).The reaction of allyltitanocenes, generated by the reductive titanation of allylic sulfides or allylic alcohol derivatives with a titanocene(II) species, with phenyl and sterically hindered alkyl methyl ketones produced anti tertiary homoallylic alcohols with complete diastereoselectivity. Even when sterically less congested methyl ethyl ketone and methyl vinyl ketone were employed, the anti homoallylic alcohols were obtained with unprecedented high diastereoselectivity. The observed anti selectivity suggests that the reaction proceeds by the addition of primary (E)-sigma-allyltitanocenes to ketones through chairlike cyclic transition states.
Yatsumonji
Yasutaka
Y
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
Nishimura
Takuya
T
Tsubouchi
Akira
A
Noguchi
Keiichi
K
Takeda
Takeshi
T