Synthesis of substituted Z-styrenes by Hiyama-type coupling of oxasilacycloalkenes: application to the synthesis of a 1-benzoxocane

Abstract

Several Hiyama cross-coupling reactions of oxasilacycloalkenes and aryl iodides are described that produce trisubstituted Z-styrenes in moderate to excellent yields. Both electron-rich and electron-poor aryl iodides are tolerated in the cross-coupling reaction. The oxasilacycloalkene coupling partners were prepared by ruthenium-catalyzed intramolecular anti-hydrosilylation of alkynols. One of the cross-coupling products was converted to a 1-benzoxocane, albeit in low yield, using an intramolecular Buchwald–Hartwig etherification. The cyclic ether produced contains the carbon skeleton of heliannuol A.

Transition Metal Catalyzed Hiyama Cross-Coupling: Recent Methodology Developments and Synthetic Applications

“…The substituted Z -styrene derivative, obtained by Hiyama coupling of 171 and 172 using Pd 2 (dba) 3 (2–3 mol%) catalyst and tetrabutylammonium fluoride (TBAF) in THF solvent, underwent intramolecular Buchwald–Hartwig etherification using 10 mol% Pd 2 (dba) 3 catalyst and 10 mol% Q-Phos ligands at 80 °C for 24 h. NaO t -Bu was selected as a suitable base in toluene for corresponding etherification reaction to afford the maximum (10%) yield of benzoxocane 174 along with 175 as the major product ( Scheme 65 ). The hydrogenation of benzoxocane 174 using Pd/C in ethanol gave 176 in 44% yield [ 209 ].…”

Eight-Membered Rings With One Oxygen Atom

“…One of them discloses the preparation of the natural compound helianane 82 (Scheme 1). [91][92][93] Asymmetric total synthesis of trilobacin 87 was achieved through a multistep strategy starting from glycolate oxazolidinone 83 and undecanal. Initially, it involves a 13-step sequence for the formation of the a,a 0 -cis-oxocene 85 that includes a ring-closing metathesis promoted by 1st generation Grubbs catalyst [bis(tricyclohexylphosphine)benzylidene ruthenium (IV) dichloride] (Grubbs I, 84).…”

“…at 90 C in a 4:1 mixture of DMF:water for 4 h. 150 Intramolecular Buchwald-Hartwig etherification of bromoalcohol 167 catalyzed by Pd(dba) 2 with Q-Phos and sodium t-butoxide provided benzoxocine 168 in very low yield along with debrominated 169 as major product (Scheme 19). 92 The synthesis of the eight-membered ring of natural (+)-laurendecumallene B 172 involved palladium-catalyzed cyclization of cyclic propargyl carbonate 170 using Pd 2 (dba) 3 and dppf in the presence of 3 equiv. of water in DMF.…”