A multifaceted phosphate tether: application to the C1-C14 subunit of dolabelides A-D

Novel Synthesis of Trisubstituted Olefins for the Preparation of the C16-C30 Fragment of Dolabelide C

A silicon-tether ring-closing metathesis strategy is reported for the synthesis of trisubstituted olefins flanked by allylic or homoallylic alcohols, which are difficult to obtain by classical ring-closing or cross-metathesis reactions. In addition, a novel Peterson olefination reaction has been developed for the preparation of the allyldimethylsilane precursors, which are versatile synthetic intermediates. This method was then applied to the synthesis of the C16-C30 fragment of dolabelide C.

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.

Crotylboron-based synthesis of the polypropionate units of chaxamycins A/D, salinisporamycin, and rifamycin S

Syntheses of the C(15)-C(27) fragments of chaxamycins A/D, rifamycin S, and the C(12)-C(24) fragment of salinisporamycin have been accomplished in 10 steps from commercially available starting materials. Three crotylboron reagents were utilized to construct the seven contiguous stereocenters in these fragments with excellent stereoselectivity.

Highly demanding cross-metathesis in the synthesis of the C16-C30 fragment of dolabelide C

A highly demanding cross-metathesis (CM) reaction for the formation of the C24-C25 trisubstituted olefin of dolabelide C has been optimized. A difference in reactivity between the E and Z enone isomers in this reaction was uncovered, and the selection of the Z isomer of the starting enone was critical for the success of the cross-metathesis. Application to the synthesis of the C16-C30 fragment of dolabelide C is reported.

Phosphate tether-mediated approach to the formal total synthesis of (-)-salicylihalamides A and B

A concise formal synthesis of the cytotoxic macrolides (-)-salicylihalamides A and B is reported. Key features of the synthetic strategy include a chemoselective hydroboration, highly regio- and diastereoselective methyl cuprate addition, Pd-catalyzed formate reduction, and an E-selective ring-closing metathesis to construct the 12-membered macrocycle subunit. Overall, two routes have been developed from a readily prepared bicyclic phosphate (4 steps), a 13-step route and a more efficient 9-step sequence relying on regioselective esterification of a key diol.

Total synthesis of dolabelide C: a phosphate-mediated approach

The first synthesis of dolabelide C (1), a cytotoxic marine macrolide, is reported utilizing a phosphate tether-mediated approach. Bicyclic phosphates (S,S,S(P))-5 and (R,R,R(P))-5 serve as the central building blocks for the construction of two major 1,3-anti-diol subunits in 1 through selective cleavage pathways, regioselective olefin reduction, and cross-metathesis. Overall, phosphate-mediated processes provided copious amounts of both major subunits allowing for a detailed RCM macrocyclization study to the 24-membered macrolactone 1.

Stereoselective synthesis of a model C(18)-C(35) spiroketal fragment of integramycin

A highly stereoselective synthesis of a model C(18)-C(35) spiroketal unit (7) of integramycin has been accomplished via an enantioselective stannyl-crotylboration reaction and an N-iodosuccinimide-mediated spiroketalization of 19a.

A concise, phosphate-mediated approach to the total synthesis of (-)-tetrahydrolipstatin

An efficient synthesis of (-)-tetrahydrolipstatin (THL) is reported. This method takes advantage of a phosphate tether-mediated, one-pot, sequential RCM/CM/hydrogenation protocol to deliver THL in eight total steps from a readily prepared (S,S)-triene. The strategy incorporates selective cross-metathesis, regioselective hydrogenation, regio- and diastereoselective cuprate addition, and Mitsunobu inversion for installation of the C5 formamide ester subunit.

Divalent and Multivalent Activation in Phosphate Triesters: A Versatile Method for the Synthesis of Advanced Polyol Synthons

The construction of mono- and bicyclic phosphate trimesters possessing divalent and multivalent activation and their subsequent use in the production of advanced polyol synthons is presented. The method highlights efforts to employ phosphate tethers as removable, functionally active tethers capable of multipositional activation and their subsequent role as leaving groups in selective cleavage reactions. The development of phosphate tethers represents an integrated platform for a new and versatile tether for natural product synthesis and sheds light on new approaches to the facile construction of small molecules.

One-pot o-nitrobenzenesulfonylhydrazide (NBSH) formation-diimide alkene reduction protocol

A one-pot protocol for the formation of 2-nitrobenzenesulfonylhydrazide (NBSH) from commercial reagents and subsequent alkene reduction is presented. The transformation is operationally simple and generally efficient for effecting diimide alkene reductions. A range of 16 substrates have been reduced, highlighting the unique chemoselectivity of diimide as a reduction system.

A multifaceted phosphate tether: application to the C15-C30 subunit of dolabelides A-D

Construction of the C15-C30 subunit of dolabelide utilizing a temporary phosphate tether is described. Two routes are reported that make use of the orthogonal protecting- and leaving-group properties innate to phosphate esters. One route relies on a selective terminal oxidation, while a second utilizes a CM/selective hydrogenation sequence. Both routes depend on a highly regio- and diastereoselective cuprate addition to set the requisite stereochemistry at C22.