Stereoselective Construction of Spiro-Fused Tricyclic Frameworks by Sequential Reaction of Enynes, Imines, and Diazoalkenes with Rh(I) and Rh(II) Catalysts

Abstract

Stereoselective construction of spiro-fused tricyclic compounds from enynes having a tethered imine with diazoalkenes was achieved by Rh(I)- and Rh(II)-catalyzed sequential reactions. This method consists of three reactions, i.e., Rh(I)-catalyzed cyclization of enynes with a tethered imine, Rh(II)-catalyzed cyclopropanation with diazoalkenes, and Cope rearrangement. Notably, the sequential reactions can be operated in one pot, in which Rh(I) and Rh(II) catalysts work in relay without any serious catalyst deactivation to afford the spirocycles in a stereoselective manner.

Rhodium(I)‐Catalyzed Enantioselective Cyclization of Enynes by Intramolecular Cleavage of the Rh−C Bond by a Tethered Hydroxy Group

“…[13] On the other hand, in the cyclization of (S)-1j using (S)-H 8 -BINAP (a mismatched pair), the formation of the rhodacycle i-d should be preferred to that of the rhodacycle i-c [Eq. (6)]. H owever,t he steric repulsion between the substituent Rand the pyrrolidine ring in ii-d would retard to form (S)-2e.Asaresult, in this case,the reaction would proceed through not only ii-d but also ii-c, resulting in adecrease in ee of the product.…”

“…[3a,b] Tanaka and coworkers also reported two types of enantioselective intramolecular cyclizations:o ne is rhodium(I)-catalyzed [2+ +2+ +2] cycloaddition of enynes with atethered carbonyl group [4] and the other is rhodium(I)-catalyzed cyclization of enynes through sp 3 C À Hb ond activation. [5] Herein, we report ar hodium(I)-catalyzed enantioselective intramolecular cyclization of enyne, [6] having ah ydroxy group in the tether,t o afford ac yclic compound possessing ac hiral quaternary carbon center [Eq. (2)].…”

Methodology for the Construction of the Bicyclo[4.3.0]nonane Core

“…Enyne metathesis has found an increasing interest in the synthesis of natural products (see Scheme 24) [80][81][82][83][84]. It has found significant use in the synthesis of larger ring systems [85][86][87][88][89] and hetereocyclic systems [90][91][92][93][94][95], but only occasionally in the synthesis of hydrindanes [96][97][98][99]. Palladium, platinum, gold, and ruthenium have been found to be the catalysts of choice for this class of reactions.…”

Cobalt(I)-Catalyzed Reductive Cyclization of Enynes and Diynes Using Hydrogen Gas as a Reductant

“…A cationic Co­(I) catalyst 7 was formed from the reduction of CoBr 2 ·6H 2 O by Zn in the presence of a ligand and NaBAr F 4 . Oxidative addition of substrate 1 to Co­(I) catalyst 7 produced cobaltacycle intermediate I , which is a common intermediate in reductive cyclization catalyzed by a transition-metal catalyst. − Then, σ-bond metathesis between I and H 2 occurred to give intermediate II , , from which reductive elimination afforded product 2 along with the regeneration of Co­(I) catalyst 7 . We speculate that a Xantphos-type ligand operates as a tridentate ligand in this reaction, which results in the prevention of side reactions such as isomerization and over-reduction by occupation of three coordination sites on the cobalt center …”