Caibocyclic rings

C. D. Gutsche and D. Redmore, Caibocyclic Ring Expansion Reactions, Academic Press, New York, 1968, p. 111. 

Secondary amines an easily converted into formamidines reaction with amidines (equation 24). Deprotonation and addition of electrophiles, including alkyl halides, acyl halides, aldehydes and dise-lenides, permit the introduction of various groups adjacent to the amino center, and therefore can be considered as an oxidation. Alkylation with dihalides gives intermediates which lead to new caibocyclic rings after removal of the formamidine group (equation 2S). ... 

In contrast, the related cyclizations used to form caibocyclic systems have been of limited synthetic value due to the acid sensitive nature of the derived allylic ether product (equation 1 Figure 11). The sensitivity of these caibocycles may be rationalized by considering the poor orbital oveilap between the allylic C—O bond with the adjacent ir-bond in a five-, six- or seven-membered ring. ... 

Overall, the ortho substituted 4-phenoxyquinolines generated in variation A which show activity in the primary screen demonstrate excellent curative control of wheat powdery mildew. Conversely, strong protective control was observed for active materials generated from modification of the quinoline caibocycle and active materials from quinoline heterocyclic ring modification showed little protective or curative control. Unfortunately, when compounds were prepared with curative substituents in the phenolic ring and protectant substituents in the quinoline carbocycle, relatively little wheat powdery mildew activity was observed. 

Narasaka s chiral titanium catalyst, prepared from (Pr 0)2 nCl2 and a tartrate-doived QR R)-l,l,4,4-tetraphenyl-2,3-0-(l-phenylethylidene)-l,2,3,4-butanetetrol, is utilized fw die asymmetric [2+2] cycloaddition of iV-acyl oxazolidinones to 1,2-propadienyl sulfides possessing a-substituents, which afford methylenecyclobutane derivatives with high enantiomeric purity. These chiral adducts are readily transformed to seven- and eight-membcrcd caibocycles widi chiral side chains hy the ring-cleavage reaetion and subsequent cationie cyclization of the chiral cyclobutane derivative [68] (Eq, 8A.44). 

---