Total synthesis

About: Total synthesis is a research topic. Over the lifetime, 25578 publications have been published within this topic receiving 489319 citations.

Evolution of a gram-scale synthesis of (+)-discodermolide

Abstract: An efficient, highly convergent, stereocontrolled total synthesis of the potent antimitotic agent (+)-discodermolide (1) has been achieved on gram scale. Key elements of the successful strategy include (1) elaboration of three advanced fragments from a common precursor (CP) which embodies the repeating stereochemical triad of the discodermolide backbone, (2) σ-bond installation of the Z trisubstituted olefin, exploiting a modified Negishi cross-coupling reaction, (3) synthesis of a late-stage phosphonium salt utilizing high pressure, and (4) Wittig installation of the Z disubstituted olefin and the terminal (Z)-diene.

A concise synthesis of (-)-aplyviolene facilitated by a strategic tertiary radical conjugate addition.

Abstract: Aplyviolene (1) and macfarlandin E (2, Figure 1A) are representative of the more complex members of the rearranged spongian diterpene class of natural products.[1,2] These diterpenes are structurally defined by attached cis-perhydroazulene and 6-acetoxy-2,7-dioxabicyclo[3.2.1]octan-3-one fragments. The substantial challenge in assembling these structures centers on the construction of the sensitive bicyclic lactone subunit and the formation of the C8–C14 σ-bond joining the two ring systems, a challenge augmented by the quaternary nature of C8.[3] We previously reported preparation of the lactone subunits of 1 and 2 by the synthesis of truncated congeners 3 and 4 (Figure 1A),[4] as well as the first total synthesis of aplyviolene (outlined in Figure 1B).[5] In this latter effort, the key C8–C14 σ-bond was formed by Michael addition of tertiary enolate 5 to enone 6.[6] Subsequent elaboration of product 7 provided intermediate 8, which was converted to (−)-aplyviolene along the lines of our earlier synthesis of 3. Undesirable aspects of this first-generation synthesis are the lengthy preparation of the cis-perhydroazulene unit and the need to remove the extraneous ketone carbonyl group from the product of the fragment-coupling step.

Alkyne metathesis: development of a novel molybdenum-based catalyst system and its application to the total synthesis of epothilone A and C.

Abstract: Sterically hindered molybdenum(III) amido complexes of the general type [Mo{(tBu)(Ar)N} 3 ] (1), upon treatment with CH 2 Cl 2 or other halogen donors, have been converted into highly effective catalysts for all kinds of alkyne metathesis reactions. Although the actual nature of the propagating species formed in situ is still elusive, halogen transfer to the Mo center of 1 plays a decisive role in the activation of such precatalysts. It was possible to isolate and characterize by X-ray crystallography some of the resulting molybdenum halide derivatives such as 15, 16 and 20 which themselves were shown to be catalytically active. Numerous applications illustrate the performance of the catalytic system 1/CH 2 Cl 2 which operates under mild conditions and tolerates an array of polar functional groups. The wide scope allows the method to be implemented into the total synthesis of sensitive and polyfunctional natural products. Most notable among them is a concise entry into the potent anticancer agents epothilone A (86) and C (88). The macrolide core of these targets is forged by ring closing alkyne metathesis (RCAM) of diyne 113, followed by Lindlar hydrogenation of cycloalkyne 114 thus formed. Since this strategy opens a stereoselective entry into (Z)-alkene 115, the approach is inherently more efficient than previous syntheses based on conventional RCM.

Total synthesis of 1233A

Abstract: The total synthesis of the HMG-CoA synthase inhibitor 1233A (1), starting from either (R)-pulegone (6) or diketo ester 12, is described. The key transformations included the diastereoselective [2,3] rearrangements of allylic ethers 9 and 19 to alcohols 10 and 11b, respectively, and the diastereoselective hydroboration of 11b to form 19. A Pd-mediated coupling of iodo olefin 31a with tert-butyl crotonate under newly devised conditions provides an efficient preparation of the diene portion of 1233A

The total synthesis of the polyether antibiotic X-206

Abstract: A convergent asymmetric synthesis of the polyether antibiotic X-206 has been achieved through the synthesis and coupling of the CI-C16 and C17-C37 synthons 16 and 17, respectively. All absolute stereochemical relationships within the molecule were controlled by application of recent methodological advances in asymmetric synthesis. In the synthesis of subunit 16, both the alkylation and aldol reactions of chiral imide-derived enolates were utilized to establish the five stereogenic centers at C2-C4 and C9-CIo, while the stereochemistry at C14 was indirectly controlled by the Sharpless asymmetric epoxidation. The C7 and Cl l stereocenters, which are situated at the two assemblage pints for 16, were established through internal asymmetric induction. The synthesis of the more complex c17<37 subunit 17 followed a similar strategy for absolute stereocontrol. Chiral enolate methodology was employed to define the stereogenic centers at C18, C,,, and C23 while asymmetric epoxidation was used to create the oxygen-bearing centers at C30-C31 and Cj4-C3). The remaining three stereogenic centers at Cz0, C,,, and C28 were controlled by internal asymmetric induction. The successful construction of this synthon relied upon the development of an efficient assemblage reaction in which three fragments comprising the entire carbon framework of 17 were united in