Maria del Rosario Rico Ferreira

Modified steroids: Pb(OAc)4 mediated one-pot multistage transformations of steroidal unsaturated 1,2-diols

Abstract Lead tetraacetate treatment of steroidal 1,2-unsaturated diols provided a convenient route to molecules possessing functionalities that are appropriate for the synthesis of a great variety of skeleton modified steroids, such as A-nor or A-nor-B-homosteroids, which could present interesting biological activities.

INFLUENCE OF THE SUBSTITUTION PATTERN ON THE PB(OAC)4 MEDIATED OXIDATIVE CLEAVAGE OF STEROIDAL 1,2-DIOLS

Abstract A rapid increase in molecular complexity, modulated by the substitution pattern, upon treatment of steroidal unsaturated diols with lead tetraacetate is presented. The steric and electronic factors involved in these cascade type transformations are investigated, the products serving as useful mechanistic probes.

Studies towards the taxoid diterpene ABC-ring system: practical access to highly functionalized enantiomerically pure analogues of major group representatives†

Abstract Short routes for practical syntheses of enantiopure taxoid subunits which possess oxygenation at sites appropriate for further elaboration into various members of the major taxoid families are described along with detailed structure elucidation.

Tandem glycol cleavage—intramolecular 4+2 cycloadditions mediated by Mn(OAc) 3

Abstract The Mn(OAc) 3 mediated oxidative cleavage of 1 and 2 proceeded as expected, while molecular diversity was generated upon cleavage of their unsaturated counterparts 5 and 6 via a tandem glycol cleavage/4+2 process. Minor products of the reaction were identified as the α-dicarbonyl derivative (i.e. 25 ) and the corresponding cross-conjugated hydroxy dienone (i.e. 26 ). The process tolerates a variety of substitution patterns and protecting groups. A brief comparison with the Pb(OAc) 4 initiated cascade transformations is presented.

Taxoid C-ring building blocks from Hajos–Parrish ketone. Practical synthesis of an enantiomerically pure taxoid ABC ring system

Abstract A synthesis and characterization of conveniently functionalized taxoid C-ring building blocks to be used in an A+C approach is presented. Subsequently, a four-step entry to the tricyclic taxoid ABC skeleton, which allows for a high degree of convergency and is highlighted by a stannylene-mediated coupling to link the left- and right-half moieties, followed by an intramolecular aldol reaction to effect the B-ring closure, is described.

PB(OAC)4 MEDIATED OXIDATIVE CLEAVAGE OF STEROIDAL UNSATURATED 1,2-DIOLS: INFLUENCE OF THE ANGULAR SUBSTITUTION

Abstract To evaluate the effect of angular substitution at C-10, the required precursor 2b was prepared by the methods described earlier and subjected to oxidative cleavage with lead tetraacetate.

A practical access into conveniently functionalized, homochiral C-ring system of taxuyunnanine C

Abstract The preparation of a homochiral 7-nor taxoid C-ring framework, to be used in an A+C approach for the synthesis of low oxygenation pattern taxoids with an exocyclic olefin at C(4)–(20) and oxygenation at C(14), is described. Retrosynthetic analysis associated with the preparation of 3 has been designed around the targets 11 and 15 which could be produced by functional group manipulation starting from the known hydrindenone 4, obtained with a moderate e.e. (ca. 70%). A lipase was used to perform clean and high yield saponification on its corresponding acetoxy enone, while chemical resolution of the resulting acyloins allowed straightforward access to diastereomerically pure material.

Stereoselective synthesis of an A-seco-taxoid subunit using the Aldol-annelation-fragmentation strategy

Abstract We present a concise route to an optically pure A-seco taxoid framework containing suitable oxygen functionalities for further elaboration.

A rapid entry into major groups of taxoids

We report here the construction of 3 to 12, equipped with functionalization suitable for further elaboration to various taxoids, that demonstrates the validity of our four-step synthesis of the taxoid ABC framework by the transmetallation (C10–C11)-aldol (C1–C2) route.

AN EXPEDIENT SYNTHESIS OF A CONVENIENTLY FUNCTIONALIZED OPTICALLY HOMOGENEOUS TAXOID ABC RING SYSTEM

Abstract We present a four-step A+C route to an optically pure taxoid ABC framework 3a containing suitable functionalities for further elaboration.