Phosphate-tether-mediated ring-closing metathesis for the preparation of complex 1,3-anti-diol-containing subunits

Total Synthesis of Sanctolide A and Formal Synthesis of (2S)-Sanctolide A

Two synthetic strategies employing phosphate tether-mediated one-pot sequential protocols for the total synthesis of the polyketide nonribosomal peptide macrolide, sanctolide A, and the formal synthesis of the (2S)-epimer of sanctolide A are reported. In this work, a phosphate tether-mediated one-pot sequential ring-closing metathesis/cross metathesis/substrate-controlled "H2"/tether removal approach was developed to accomplish the total synthesis of the natural product sanctolide A.

Unified Strategy for 1,5,9- and 1,5,7-Triols via Configuration-Encoded 1,5-Polyol Synthesis: Enantioselective Preparation of γ-Sulfonyl-α-silyloxyaldehydes and Iterative Julia-Kocienski Coupling

Diverse classes of natural products contain chiral 1,5-polyols, within which may be stereochemical triads of 1,5,9- and 1,5,7-triols. Biological activities associated with compounds containing these motifs warrant targeted synthetic strategies to access all stereoisomers of a 1,5-polyol family from cheap and easily accessible reagents while avoiding the need to determine configurations at each alcohol stereocenter. Here, we address these problems via design and implementation of an iterative configuration-encoded strategy to access 1,5-polyols with unambiguous stereocontrol; the coupling event exploits Julia-Kocienski reactions of enantiopure α-silyloxy-γ-sulfononitriles. These building blocks, bearing sulfone at one terminus and α-silyloxyaldehyde (in latent form) at the other, were prepared via asymmetric catalysis. An efficient scalable route to these building blocks was developed, leading to enantiopure samples in multigram quantities. Preliminary studies of acetals as the latent aldehyde functionality in the α-silyloxyaldehyde showed that Julia-Kocienski coupling of these building blocks was effective, but iterative application was thwarted during acetal hydrolysis, leading to use of nitrile to perform the latent aldehyde function. A variety of 1,5-polyols, including a 1,5,9,13-tetraol and a differentially protected 1,5,9-triol, were prepared, validating the approach. The accompanying paper describes the application of this configuration-encoded 1,5-polyol synthesis to 1,5,9- and 1,5,7-triols found in tetrafibricin.

Phosphate Tether-Mediated Ring-Closing Metathesis for the Generation of P-Stereogenic, Z-Configured Bicyclo[7.3.1]- and Bicyclo[8.3.1]phosphates

A phosphate tether-mediated ring-closing metathesis (RCM) study to the synthesis of Z-configured, P-stereogenic bicyclo[7.3.1]- and bicyclo[8.3.1]phosphates is reported. Investigations suggest that C3-substitution, olefin substitution, and proximity of the forming olefin to the bridgehead carbon of the bicyclic affect the efficiency and stereochemical outcome of the RCM event. This study demonstrates the utility of phosphate tether-mediated desymmetrization of C2-symmetric, 1,3-anti-diol-containing dienes in the generation of macrocyclic phosphates with potential synthetic and biological utility.

A Pot-Economical Approach to the Total Synthesis of Sch-725674

A pot-economical total synthesis of antifungal Sch-725674, 1, is reported. The approach takes advantage of a number of one-pot, sequential transformations, including a phosphate tether-mediated one-pot, sequential RCM/CM/chemoselective hydrogenation protocol, a one-pot tosylation/acrylation sequence, and a one-pot, sequential Finkelstein reaction/Boord olefination/acetonide deprotection procedure to streamline the synthesis route by reducing isolation and purification procedures, thus saving time. Overall, an asymmetric route has been developed that is efficiently accomplished in seven pots from phosphate (S,S)-triene and with minimal purification.

Phosphate Tether-Mediated Ring-Closing Metathesis for the Generation of Medium to Large, P-Stereogenic Bicyclo[n.3.1]phosphates

A phosphate tether-mediated ring-closing metathesis study towards the synthesis of P-stereogenic bicyclo[6.3.1]-, bicyclo[7.3.1]-, and bicyclo[8.3.1]phosphates is reported. This study demonstrates expanded utility of phosphate tether-mediated desymmetrization of C₂-symmetric, 1,3-anti-diol dienes in generating complex medium to large, P-stereogenic bicyclo[n.3.1]phosphates..

Phosphate tethers in natural product synthesis

Recent advances in phosphate tether-mediated natural product synthesis are reviewed. Synthetic approaches toward dolabelide C, (-)-salicylihalimide A, (-)-tetrahydrolipstatin, and (+)-strictifolione are included. In addition, current efforts in method development are briefly reviewed, including a detailed study on the effect of stereochemical complexity on the phosphate-mediated, diastereoselective ring-closing metathesis reaction and recent advances in multi-reaction, one-pot sequential processes mediated by the phosphate tether. Overall, this review seeks to highlight the utility of phosphate triesters to serve as multifunctional tethers with protecting group and latent leaving group characteristics and the ability to orchestrate multiple, orthogonal reaction pathways to allow for the facile synthesis of complex, bioactive small molecules and their analogs.

A modular phosphate tether-mediated divergent strategy to complex polyols

An efficient and divergent synthesis of polyol subunits utilizing a phosphate tether-mediated, one-pot, sequential RCM/CM/reduction process is reported. A modular, 3-component coupling strategy has been developed, in which, simple “order of addition” of a pair of olefinic-alcohol components to a pseudo-C₂-symmetric phosphoryl chloride, coupled with the RCM/CM/reduction protocol, yields five polyol fragments. Each of the product polyols bears a central 1,3-anti-diol subunit with differential olefinic geometries at the periphery.