Seven-membered ring generation

SEVEN-MEMBERED RING GENERATION 6.1 Unmasking the Terminal Alkene... 

An auxiliary controlled enantioselective route to generate seven-membered ring lactams 75 used the a-alkylation of cyclic hydrazide derivatives 74. Initially, 6-chloro hydrazides 73,bearing the chiral information in the M-amino-pyrrolidine function underwent amidocyclization in the presence of a base. A subse-... 

The use of cycloadditions for synthesizing medium-sized ring lactams is more or less restricted to the generation of seven-membered rings. The simplest method to generate azepinones seems to be the [6-1-1] reaction of a 1,6-dicar-boxylic acid chloride 148/152 and a phosphinimine 149, the in situ formed chloro enamine 150 underwent a Chapman rearrangement to give a cyclic imide 151/153 (Scheme 28)] [36]. 

The use of a carbene as the one-carbon component provides an alternative and efficient entry into the [4 + 2+1]-reaction manifold. Montgomery and Ni have developed a nickel-catalyzed process where the carbene is generated from trimethylsilyldiazomethane (Scheme 45).135 It is not known, however, if the seven-membered ring forms via a Cope rearrangement of a divinylcylopropane or if the metal is intimately involved in the step that leads directly to... 

Hydrolytic cleavage of a seven-membered ring occurs in the metabolism of chlordiazepoxide (5.82, Fig. 5.22,a) and other benzodiazepines (see also Sect. 11.9). The lactam ring opened metabolite 5.83 was detected in humans and dogs and is believed to be generated by hydrolysis of the intermediate lactam [181][182], However, the diazepine ring can be split by other mech-... 

A seven-membered ring oxygen heterocycle 176 could also be generated by type intramolecular metallo-ene reactions and the zinc-ene process appeared by far more efficient than the magnesium-ene. However, in the nitrogen series, type II zinc-and magne-sium-ene reactions exhibited similar efficiencies and afforded the substituted 3-methylene piperidine 177 in comparable yields (equation 86)121. 

In situ generation of an allylstannane from an allylic acetate and hexamethyldistannane results in five-membered ring formation in preference to the allyl alternative seven-membered ring (equation 243).140... 

The intramolecular 4 + 3-, 3 + 3-, 4 + 2-, and 3 + 2-cycloaddition reactions of cyclic and acyclic allylic cations have been reviewed, together with methods for their generation by thermal and photochemical routes.109 The synthetic uses of cycloaddition reactions of oxyallyl cations, generated from polybromo and some other substrates, have also been summarized seven-membered rings result from 4 + 3-cycloadditions of these with dienes.110 The use of heteroatom-stabilized allylic cations in 4 + 3-cycloaddition reactions is also the subject of a new experimental study.111 The one-bond nucleophilicities (N values) of some monomethyl- and dimethyl-substituted buta-1,3-dienes have been estimated from the kinetics of their reactions with benzhydryl cations to form allylic species.112 Calculations on allyl cations have been used in a comparison of empirical force field and ab initio calculational methods.113... 

Whittaker and co-workers805,806 have also prepared a number of terpenoid bicyclic ethers, such as isomeric 1,6-dihydrocarveols 199 (HSO3F—S02,78°C) from unsaturated alcohols or diols.805 806pura-Menth-l-en-9-ol and a related diol afforded the seven-membered ring systems 200. The oxolane moiety in compound 201 was generated from the corresponding unsaturated alcohol precursor in 2 equivalents of triflic acid.807... 

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