Total Synthesis of (±)-5-Deoxystrigol via Reductive Carbon−Carbon Bond Formation

Stereo-Controlled Synthesis of Vicinal Tertiary Carbinols: Application in the Synthesis of a Diol Substructure of Zaragozic Acid, Pactamycin and Ryanodol

A novel and flexible approach for the stereo-controlled synthesis of vicinal tertiary carbinols is reported. The developed strategy featured a highly diastereoselective singlet-oxygen (O2 1 ) [4+2] cycloaddition of rationally designed cyclohexadienones (derived from oxidative dearomatization of the corresponding carboxylic-acid appended phenol precursors), followed by programmed "O-O" and "C-C" bond cleavage. In doing so, a highly functionalized and versatile intermediate was identified and prepared in synthetically useful quantity as a plausible precursor to access a variety of designed and naturally occurring vicinal tertiary carbinol containing compounds. Most notably, the developed strategy was successfully applied in the stereo-controlled synthesis of advanced core structures of zaragozic acid, pactamycin and ryanodol.

Application of The Dess-Martin Oxidation in Total Synthesis of Natural Products

Dess-Martin periodinane (DMP), a commercially available chemical, is frequently utilized as a mild oxidative agent for the selective oxidation of primary and secondary alcohols to their corresponding aldehydes and ketones, respectively. DMP shows several merits over other common oxidative agents such as chromiumand DMSO-based oxidants; thus, it is habitually employed in the total synthesis of natural products. In this review, we try to underscore the applications of DMP as an effective oxidant in an appropriate step (steps) in the multi-step total synthesis of natural products.

Pd-Catalyzed Alkene Difunctionalization Reactions of Enolates for the Synthesis of Substituted Bicyclic Cyclopentanes

Palladium-catalyzed alkene difunctionalization reactions between alkenes bearing tethered aryl or alkenyl triflates and enolate nucleophiles are described. The transformations form two C-C bonds, a ring, and up to two stereocenters, while producing substituted cyclopentane derivatives that contain appended carbonyl functionality. Products are formed with up to >20:1 diastereoselectivity, and formation of sterically congested bonds between quaternary carbon atoms is feasible.

Strigolactones: mediators of osmotic stress responses with a potential for agrochemical manipulation of crop resilience

After quickly touching upon general aspects of strigolactone biology and functions, including structure, synthesis, and perception, this review focuses on the role and regulation of the strigolactone pathway during osmotic stress, in light of the most recent research developments. We discuss available data on organ-specific dynamics of strigolactone synthesis and interaction with abscisic acid in the acclimatization response, with emphasis on the ecophysiological implications of the effects on the stomatal closure process. We highlight the importance of considering roots and shoots separately as well as combined versus individual stress treatments; and of performing reciprocal grafting experiments to work out organ contributions and long-distance signalling events and components under more realistic conditions. Finally, we elaborate on the question of if and how synthetic or natural strigolactones, alone or in combination with crop management strategies such as grafting, hold potential to maximize crop resilience to abiotic stresses.

Total synthesis of avenaol

Avenaol, isolated from the allelopathic plant black oat, was the first C₂₀ germination stimulant related to strigolactones. Structurally, it consisted of a bicyclo[4.1.0]heptanone skeleton containing a cyclopropane ring bearing three main chains projecting in the same direction (i.e. all-cis-substituted cyclopropane). Herein, we report the total synthesis of avenaol using a robust strategy involving the formation of an all-cis-substituted cyclopropane via an alkylidenecyclopropane. The key factors in the success of this total synthesis include the Rh-catalysed intramolecular cyclopropanation of an allene, an Ir-catalysed stereoselective double-bond isomerisation, and the differentiation of two hydroxymethyl groups via the regioselective formation and oxidation of a tetrahydropyran based on the reactivity of a cyclopropyl group. This strategy effectively avoids the undesired ring opening of the cyclopropane ring and the formation of a caged structure. Furthermore, this study confirms the proposed structure of avenaol, including its unique all-cis-substituted cyclopropane moiety.Avenaol is a potent germination stimulant that can be extracted from black oat. Here, the authors report the total synthesis of avenaol by developing a strategy to access all-cis-substituted cyclopropanes.

Synthesis of stable isotopically labelled 3-methylfuran-2(5H)-one and the corresponding strigolactones

Conventional synthetic procedures of strigolactones (SLs) involve the independent synthesis of ring ABC and ring D, followed by a coupling of the two fragments. Here we prepared three kinds of stable, isotopically labelled D-ring analogues productively using a facile protocol. Then, a coupling of the D-rings to ring ABC produced three isotope-labelled SL derivatives. Moreover, (+)-D3-2'-epi-1A and (-)-ent-D3-2'-epi-1A with high enantiomeric purity were obtained via chiral resolution.

New strigolactone analogs as plant hormones with low activities in the rhizosphere

Strigolactones (SLs) are known not only as plant hormones, but also as rhizosphere signals for establishing symbiotic and parasitic interactions. The design of new specific SL analogs is a challenging goal in understanding the basic plant biology and is also useful to control plant architectures without favoring the development of parasitic plants. Two different molecules (23 (3'-methyl-GR24), 31 (thia-3'-methyl-debranone-like molecule)) already described, and a new one (AR36), for which the synthesis is presented, are biologically compared with the well-known GR24 and the recently identified CISA-1. These different structures emphasize the wide range of parts attached to the D-ring for the bioactivity as a plant hormone. These new compounds possess a common dimethylbutenolide motif but their structure varies in the ABC part of the molecules: 23 has the same ABC part as GR24, while 31 and AR36 carry, respectively, an aromatic ring and an acyclic carbon chain. Detailed information is given for the bioactivity of such derivatives in strigolactone synthesis or in perception mutant plants (pea rms1 and rms4, Arabidopsis max2 and, max4) for different hormonal functions along with their action in the rhizosphere on arbuscular mycorrhizal hyphal growth and parasitic weed germination.

New synthesis of A-ring aromatic strigolactone analogues and their evaluation as plant hormones in pea (Pisum sativum)

A new general access to A-ring aromatic strigolactones, a new class of plant hormones, has been developed. The key transformations include in sequence ring-closing metathesis, enzymatic kinetic resolution and a radical cyclization with atom transfer to install the tricyclic ABC-ring system. The activity as plant hormones for the inhibition of shoot branching in pea of various analogues synthesized by this strategy is reported.