Synthesis of Seven- and Eight-Membered Rings

Irradiation of enamines (249) results in processes related to reduction and cyclization reactions with the participation of the enamine /3-carbon atom (82JOC482). A benzazepine derivative (250) was isolated as one of the products. Enamines (251) interact with aldehydes in a smooth reaction and give diazepines [84CPB3274 91KFZ(11)16]. Benzodiazepine derivatives can be obtained in a similar fashion (95KGS336). 

Enaminoketones (252) can undergo cyclization in several different ways depending on reaction conditions. Thus, in the presence of acetic 

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Examples of the synthesis of seven- and eight-membered rings are shown in Eqs. (129-130). ... 

The relative ease of ring formation from dienes decreases in the order six->seven->five-membered rings. Hoshi et al. [138] have recently reported the synthesis of a number of disilacycloalkenes via RCM of bis(allyldimethyl-silyl)substituted compounds, with the ruthenium vinylcarbene complex Cl2(PCy3)2Ru(=CHCH=CPh2) used as a catalyst. Successful formation of seven-and eight-membered rings has been achieved under mild reaction conditions. 

In this chapter we provide an overview of studies originating from the above work and directed at the design and development of three new metal-catalyzed cycloaddition reactions, namely the [5+2] cycloaddition of vinylcyclopropanes (VCPs) and rc-systems, the [6+2] cycloaddition of vinylcyclobutanones and re-systems, and the three-component, [5+2+1] cycloaddition of VCPs, rc-systems, and CO. These new reactions provide fundamentally new approaches to a range of problems in seven- and eight-membered ring synthesis. 

M. E. Butcher, J. C. Ireson, J. B. Lee, and M. J. Tyler, Seven and eight membered ring sugars and related systems The synthesis of some septanose rings from dioxepans, Tetrahedron, 33 (1977) 1501-1507. 

Steve Martin of UT Austin has reported (J. Org. Chem. 68 8867,2003) a detailed study of the synthesis of bridged azabicyclic structures via ring-closing alkene metathesis. Some examples of his work include the conversion of 12 to 13, efficiently forming six, seven and eight membered rings. He also demonstrated five-membered ring formation with the conversion of 14 to IS, which has the cocaine skeleton. 

The synthesis of polycyclic ethers with variable ring sizes can be conducted by two-directional double ring-closing metathesis. This methodology was used to prepare, in one-step, the tricyclic ether 73, which has a six-, seven-, and eight-membered ring (Scheme 9) <2000AGE372>. 

The diversity-oriented synthesis of enantiomerically pure seven- and eight-membered ring systems was reported from easily accessible naturally occurring. Y-amino acids and their readily prepared derivatives as chiral synthons <2007JC0321>. Intramolecular Mitsunobu reaction was used as a key transformation to construct the 1,4-diazocines 224 (Scheme 27) and 1,4-oxazocines 225 (Scheme 28) <2007JC0321>. 

Synthesis of Polyspiroketals Containing Five-, Six-, Seven-, and Eight-Membered Rings... 

Seven- and Eight-membered Rings.- A new total synthesis of zoa-patanol has been published which uses as the key step an acid-catalysed intramolecular epoxide opening reaction (see Scheme... 

Holt and co-workers applied their ring-closing metathesis strategy for the synthesis of six-, seven-, and eight-membered ring annulated carbohydrate systems to synthesize a number of enantiomerically pure annulated carbohydrate systems containing nine-membered ring... 

As reported in CHEC-II(1996) <1996CHEC-II(7)921>, compounds with a central seven- or eight-membered ring can be prepared by cyclization of an 0-allyl oxime. However, only one report in this area could be found, the full paper by Wang and Wong on their previously described synthesis of 108 <1995T6941>. 

The synthesis of oxygen-containing seven- or eight-membered rings by IMSC reaction has been little studied as compared to their five- and six-membered analogues. 

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