Stereoselectivity Control in the Rh(I)‐Catalyzed Conjugate Additions of Aryl and Alkenylboronic Acids to Unprotected Hydroxycyclopentenones.

Abstract

Cyclopentane derivatives Q 0030 Stereoselectivity Control in the Rh(I)-Catalyzed Conjugate Additions of Aryl and Alkenylboronic Acids to Unprotected Hydroxycyclopentenones. -The stereochemistry concerning the reaction of alkenylboronic acids (IV) with pentenone (I) can be tuned by the appropriate additive without the need of protecting the free hydroxyl group. -(DE LA HERRAN, G.; MBA, M.; MURCIA, M. C.; PLUMET, J.; CSAKY*,

TRIP-Catalyzed Asymmetric Synthesis of (+)-Yatein, (−)-α-Conidendrin, (+)-Isostegane, and (+)-Neoisostegane

“…Having product in hand, the second benzylic group was easily attached using a rhodium(I) catalyzed 1,4-addition to the exocyclic double bond yielding dibenzylbutyrolactone (14). 37,38 Simple hydrogenation under acidic conditions removed the benzylic hydroxyl function cleanly and provided (-)-yatein ( 10 The same reaction sequence was tested with aldehyde 15 in order to obtain the corresponding precursors for the neoisostegane natural product (6). The allylation sequence was tested under the same reaction conditions as for piperonal (11, see Table 1).…”

“…31 (−)-α-Conidendrin (8) can be easily prepared via a Friedel−Crafts alkylation under acidic conditions from the corresponding hydroxy-dibenzylbutyrolactone. 31,36 The latter key intermediate can be obtained via Rh I -catalyzed 1,4addition of the arylboronate 37,38 and the previously reported TRIP-catalyzed asymmetric allylation. 13 As the first synthetic target, we picked isostegane (5, see Scheme 3 for forward synthesis).…”

“…With product 12 in hand, the second benzylic group was easily attached using a rhodium(I)-catalyzed 1,4-addition to the exocyclic double bond, yielding dibenzylbutyrolactone 14. 37,38 Simple hydrogenation under acidic conditions removed the benzylic hydroxyl function cleanly and provided (−)-yatein (10) via a four-step synthetic route. This compound differs from stegane only by the axial chirality of the biaryl system and can be interconverted into the latter by simply heating it up (200 °C, 39% yield, 61% recovered isostegane).…”