Copper-catalyzed ring expansion

Substituted 4,5-dihydro-l,2-dithiins were obtained as by-products in the copper-catalyzed ring expansion of vinyl... 

In contrast to aforementioned silacyclopropenes, copper-catalyzed ring expansion was achieved with silyloxy-orboryl-substituted silacyclopropenes (Scheme7.34). 101,104 Simply changing the ether substituent from an alkyl group to a silyl group enabled oxasilacyclopentene formation from 112b. These results reveal that the reactivity modes of the silacyclopropene are controlled by the identity of the substituent. 

Recently, two methodologies have been published that use very unique approaches to synthesize 4,5,6,7-tetrahydrothieno[3,2-c]pyridine, a key thiophene-containing intermediate en route to clopidogrel. One such approach is the copper-catalyzed ring expansion of vinyl thiiranes followed by oxidation and subsequent removal of the amine protecting group. ... 

Finally, multiple reports detailing ring-opening reactions of 2H-azirines were disclosed. Select examples include photocatalytic formal [3 + 2] cycloaddition of 2H-azirines with alkynes (14AG(I)5653) and copper-catalyzed ring expansion of terminal alkynes with 2H-azirines (14OL4806) to aflbrd pyrroles. Likewise, pyridines were produced in either a transition-metal-free... 

A successful tandem catalysis was found by Barluenga et al. [80]. In the presence of [Cu(CHjCN)4][BF ], vinyldiazoacetates 113 readily undergo a copper(I)-cata-lyzed cyclopropanation with diazo compounds 114 and a copper(I)-catalyzed ring expansion of the cyclopropane intermediate 115 to substituted cyclobutenes 116 (Scheme 5.77). Changing the diazo compounds 114 to iminoiodinanes 117 leads to substituted 2-azetines 118 (Scheme 5.78) [81]. As shown in Scheme 5.79, the process... 

More recently, Naidu and West have utilized a ring expansion reaction of spiro azetidinium ylide 167 in the synthesis of pyrrolizidine alkaloids. Spiro azetidinium ylide 167 is generated through a Cu(acac)2-catalyzed intramolecular reaction of a copper carbene complex with a pendant amino moiety. Subsequent [l,2]-shift gives fused bicyclic products 168 and 169 as a diastereomeric mixture. Each diastereomer was further converted to naturally occurring pyrrolizidines ( )-turneforcidine and ( )-platynecine, respectively (Scheme 18). ... 

Metal-promoted vinylcyclopropane C3 - C5 ring expansions have been reported. Thus, ethyl 2-methoxy-2-vinylcyclopropanecarboxylate 393 rearranged to a 2 1 mixture of 3-methoxy-2-cyclopentenecarboxylate 396 and 3-methoxy-3-cyclopentene-carboxylate 397 on heating at 160 °C in the presence of catalytic amounts of copper bronze or copper(I) chloride in contrast, platinum and rhodium complexes catalyzed... 

The Buchwald group reported an interesting copper-catalyzed lactam /V-arylation/ ring-expansion cascade wherein compound 669 reacted with 2-azetidinone 670 in the presence of Cul and K2C03 to give 671 in 96% yield (Scheme 110) (04JA3529). 

A range of 3-pyrrolines could be synthesized from conjugated dienes with common nitrene precursors catalyzed by [Cufhfacaclj] via intermolecular [4h-1] cycloaddition. Good to excellent cisltmns selectivity could be obtained when 1,4-disubstituted dienes are used as substrates. The cis or trans preference depends on the nature of the substituents of the substrates. Mechanistic studies disclose that this transformation proceeds through diene aziridination and subsequent ring expansion. The [Cufhfacaclj] catalyst shows higher activity than other copper catalysts [41] (Scheme 8.17). 

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