Oxocarbenium intermolecular reaction

Estimates of effective molarities in general acid catalysis of acetals require the analogous intermolecular reaction to be observable and therefore, as we have seen in the previous section, for the oxocarbenium ion to be particularly stable. The termolecular processes corresponding to the hydrolysis of salicyl... 

The intermolecular reaction of oxocarbenium ions with simple alkenes, less reactive carbon nucleophiles, is generally slow and inefficient. A recent paper has described that the (la)-promoted intermolecular reaction of acetals with vinylcyclopropane (22) gives 3,6-heptadienyl ethers (23) with high E selectivity [74]. The allylation mechanism involves the formation of a cyclopropylmethyl cation intermediate and its ring opening (Scheme 9.21). Homoallylstannane (24) also adds to the oxocarbenium ion generated from benzaldehyde dimethyl acetal and (la) [75]. 

The dihydropyran 88 served as the precursor for an oxocarbenium ion that was utilized as the acceptor for the intermolecular Hosomi-Sakurai reaction [53, 54]. Utilizing a second Hosomi-Sakurai reaction, pyran 88 was synthesized as outlined in Scheme 17 [53, 54]. Easy accessible MOM protect-... 

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