José Ignacio Candela Lena

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.

Oxidative cleavage of unsaturated 1,2-diols using chiral lead-tetracarboxylates obtained by in situ metathesis

Abstract A combination of an acetate metathesis/cascade transformations process, providing ring enlarged systems decorated with a chiral auxiliary, is presented. The use of a chiral carboxylic acid, such as ( S )-2-acetoxypropionic acid, gives diastereomeric mixtures when performed in the racemic series, offering the possibility of a chemical resolution.

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.

Iodobenzene diacetate-mediated hetero-domino transformations

Abstract Treatment of a series of unsaturated diols with iodobenzene diacetate (PhI(OAc) 2 ), in various solvents gave cyclic ene-acetals by a sequential oxidative cleavage-intramolecular [4+2] cycloaddition. The reaction is easy to perform, can be scaled up safely and occurs efficiently irrespective of the diol stereochemistry.

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 hetero-domino transformations: can any unsaturated 1,2-diol be regarded as a substrate?

We report the oxidative cleavage of unsaturated diols 6 and 7 derived from monocyclic precursors, used as substrates to determine the limits of the olefin as a source of diversity.

Lead tetraacetate mediated domino reactions on (R)-(−)-carvone-derived bicyclic unsaturated 1,2-diols and further rearrangements

Abstract Carvone derived octaline diols 1 and 2 were subjected to Pb(OAc)4-mediated glycol fission conditions. The isolable ‘half-cascade’ intermediate 3 was subjected to ozonolysis in methylene chloride, and subsequent basic treatment, providing bis-angularly substituted bicyclic lactone 5 via an intramolecular Cannizzaro type oxidoreduction. The ring expanded products 4 and 6 subjected to basic treatment afforded bicyclic aldols 8 and 7, respectively, via a fused-to-bridged ring system interchange. The methods described here represent efficient approaches to a variety of conveniently functionalized chiral backbones offering chemoselectivity. The mechanistic pathways involved in both the oxidative cleavage induced domino transformations and in the base-induced ring-system interchange reactions are discussed.

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.