The Joy and Challenge of Small Rings Metathesis

Abstract

carbenes · cycloisomerization · homogeneous catalysis · metathesisOlefin metathesis (from the Greek word metaqesiz, meaning transposition) is an alkylidene exchange between two reacting fragments mediated by transition-metal alkylidene complexes. [1] Recent decades have seen burgeoning interest in olefin metathesis, resulting in a number of elegant applications. Using this tool, chemists can now efficiently synthesize an impressive range of molecules that only a decade ago required significantly longer and tedious routes.[1] Several types of olefin metathesis have been identified so far; among them, ring-closing metathesis (RCM) and cross-metathesis (CM) have been widely applied in the synthesis of biologically active compounds (Scheme 1). Ring-closing metathesis occurs when a diene undergoes intramolecular metathesis to afford a cyclic olefin. Analogous intramolecular reaction of an enyne is sometimes called enyne cycloisomerization or enyne RCM.[2] Ring-closing metathesis of dienes and enynes represent an attractive and powerful tool for the formation of medium and large cycles (! 5-membered rings). However, it is generally acknowledged that small (three-and fourmembered) and strained rings cannot be formed by RCM.

Linear Tetraquinanes by Microwave Assisted [3+2] Cycloaddition and Ring‐Rearrangement Metathesis

“…It seems that, there are many examples for the synthesis of such compounds involving non-metathetic routes having a large number of steps. However, here we have used RRM [12][13][14][15][16][17][18][19][20] route to drastically reduce the number of steps. As shown in Figure 2, we compared the other strategies [1,21,22] with our short synthetic routes involving RRM.…”

Synthetic Studies to exo‐Ring‐Junction based Fused 5/5/n‐Tricyclic Systems: Access to A, B, C‐Ring System of Longeracinphyllin A, Himalenine D, and Daphnipaxiamine A.

“…In view of our continuous interest in CÀ C bond formation reactions [44][45][46][47][48] such as olefin-metathesis, [49][50][51][52][53][54][55][56][57][58][59] we envisioned a new synthetic strategy to assemble fused 5/5/n (n = 6, 7, 8)tricyclic systems by adopting a simple and rapid protocol which involve RRM as a key step and exo-dicyclopentadiene-1-one (exo-DCPD-1-one; 11) as a key building block.…”

Synthesis of Macrocyclic Musk‐Like Compounds through Ring‐Expansion Metathesis and Tebbe Olefination as Key Steps

“…It has been observed that the olefin metathesis [24][25][26][27][28][29][30][31] is useful tool in the synthesis of macrocyclic musks. One of the most crucial processes for creating cyclic molecules, including medicines, natural products, musk macrolactones, and other chemicals, is ring-closing metathesis (RCM).…”