Use of epoxidation and epoxide opening reactions for the synthesis of highly functionalized 1-oxaspiro[4.5]decan-2-ones and related compounds

Ruthenium-catalyzed hydrohydroxyalkylation of acrylates with diols and α-hydroxycarbonyl compounds to form spiro- and α-methylene-γ-butyrolactones

Under the conditions of ruthenium(0)-catalyzed hydrohydroxyalkylation, vicinal diols 1a-1l and methyl acrylate 2a are converted to the corresponding lactones 3a-3l in good to excellent yield. The reactions of methyl acrylate 2a with hydrobenzoin 1f, benzoin didehydro-1f, and benzil tetradehydro-1f form the same lactone 3f product, demonstrating that this process may be deployed in a redox level-independent manner. A variety of substituted acrylic esters 2a-2h participate in spirolactone formation, as illustrated in the conversion of N-benzyl-3-hydroxyoxindole 1o to cycloadducts 4a-4h. Hydrohydroxyalkylation of hydroxyl-substituted methacrylate 2i with diols 1b, 1f, 1j, and 1l forms α-exo-methylene-γ-butyrolactones 5b, 5f, 5j, and 5l in moderate to good yield. A catalytic cycle involving 1,2-dicarbonyl-acrylate oxidative coupling to form oxaruthenacyclic intermediates is postulated. A catalytically competent mononuclear ruthenium(II) complex was characterized by single-crystal X-ray diffraction. The influence of electronic effects on regioselectivity in reactions of nonsymmetric diols was probed using para-substituted 1-phenyl-1,2-propanediols 1g, 1m, and 1n and density functional theory calculations.

Total synthesis of (+)-scyphostatin featuring an enantioselective and highly efficient route to the side-chain via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)

(+)-Scyphostatin (1) was synthesized via (i) construction of a side-chain 3b of > or = 98% purity in 19% yield in eleven steps featuring ZACA reaction, Negishi coupling, and HWE olefination, (ii) an asymmetric synthesis of a fully protected core 4 from 10a, and (iii) a three-step assembly of 1 in 42% yield.

Enantioselective Synthesis of Natural Polyoxygenated Cyclohexanes and Cyclohexenes from [(p-Tolylsulfinyl)methyl]-p-quinols

Exploitation of the beta-hydroxysulfoxide fragment present in a number of enantiomerically pure (SR)- and (SS)-[(p-tolylsulfinyl)methyl]-p-quinols allowed chemo- and stereocontrolled conjugate additions of different organoaluminium reagents to the cyclohexadienone moiety. The same fragment was also shown to act as an efficient chiral masking carbonyl group, after oxidation to sulfone and retroaddition in basic medium, with elimination of methyl p-tolyl sulfone. Through the use of both transformations as key steps, enantiocontrolled syntheses of different natural products-such as the two enantiomers of dihydroepiepoformin, (-)-gabosine O, (+)-epiepoformin, (-)-theobroxide and (+)-4-epigabosine A (an epimer of the natural product gabosine A)-has been achieved. The presence of the beta-hydroxy sulfone moiety makes the cyclic structures rigid, allowing a number of stereoselective transformations such as carbonyl reductions, enone epoxidations or cis-dihydroxylations, en route to the natural structures. The observed selectivities were dependent on the particular substitution in each substrate, providing evidence of a strong influence of remote groups on the preferred approach of the reactants to the reactive conformations. An advanced precursor of natural (+)-harveynone was also synthesized, but the isolation of the natural product was not possible because of the instability of the corresponding enone, containing a triple bond, under the basic conditions necessary to eliminate the beta-hydroxy sulfone. This demonstrated that the limitations of the use of the beta-hydroxy sulfoxide as a chiral protecting carbonyl group were dependent on the relative stabilities of the final targets in the presence of the required base.

Short and Efficient Route to the Fully Functionalized Polar Core of Scyphostatin

[reaction: see text]. Diastereoselective oxidative dearomatization of benzopyran 5 to the corresponding p-quinol 9b allows a fast, efficient, and versatile entry to scyphostatin's polar epoxycyclohexenone moiety as demonstrated by the preparation of its palmitoyl analogue 16 (R = (CH2)14CH3).