Catalytic cross-metathesis is a central transformation in chemistry, and yet, corresponding methods for stereoselectively generating acyclic trisubstituted alkenes in either isomeric form do not exist. The key problems are lack of chemoselectivity, namely, the preponderance of side reactions involving only the less hindered starting alkene, ensuing nonproductive processes of homo-metathesis byproducts, and formation of short-lived methylidene complexes. In contrast, in catalytic cross-coupling, another widely used process, substrates are more distinct and homocoupling is less of a problem. Here, we show that through cross-metathesis reactions involving E- or a Z-trisubstituted alkenes, easily prepared from commercially available starting materials by cross-coupling processes, many otherwise desirable and difficult-to-access linear E- or Z-trisubstituted alkenes can be synthesized efficiently and in exceptional stereoisomeric purity (up to >98% E or 95% Z). Utility is highlighted through concise stereoselective syntheses of biologically active compounds such as indiacen B (anti-fungal) and coibacin D (anti-inflammatory).
A convergent
diastereo- and enantioselective total synthesis of
anticancer and antifungal macrocyclic natural product disorazole C1 is reported. The central feature of the successful route
is the application of catalytic Z-selective cross-metathesis
(CM). Specifically, we illustrate that catalyst-controlled stereoselective
CM can be performed to afford structurally complex Z-alkenyl–B(pin) as well as Z-alkenyl iodide
compounds reliably, efficiently, and with high selectivity (pin =
pinacolato). The resulting intermediates are then joined in a single-step
operation through catalytic inter- and intramolecular cross-coupling
to furnish the desired 30-membered ring macrocycle containing the
critical (Z,Z,E)-triene moieties.
Get me a Z (olefin): Efficient catalytic cross‐metathesis reactions that afford Z‐disubstituted allylic silyl or benzyl ethers are reported (see scheme, MAP=monoalkoxide pyrrolide). The approach, in combination with catalytic cross‐coupling, provides a general entry to otherwise difficult‐to‐access alkyne‐containing Z olefins.
The first synthesis of (±)-tetrapetalone A-Me aglycon is described. Key bond-forming reactions include Nazarov cyclization, a ring-closing metathesis (RCM) promoted with complete diastereoselectivity by a chiral Mo-based complex, tandem conjugate reduction-intramolecular aldol cyclization, and oxidative dearomatization.
The first enantioselective total synthesis of (−)-deoxoapodine is described. Our synthesis of this hexacyclic aspidosperma alkaloid includes an efficient molybdenum-catalyzed enantioselective ring-closing metathesis reaction for desymmetrization of an advanced intermediate that introduces the C5-quaternary stereocenter. After C21-oxygenation, the pentacyclic core was accessed via an electrophilic C19-amide activation and transannular spirocyclization. A biogenetically inspired dehydrative C6-etherification reaction proved highly effective to secure the F-ring and the fourth contiguous stereocenter of (−)-deoxoapodine with complete stereochemical control.
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