M. Yoshimatsu et al., A NEW METHOD OF GENERATION OF ALPHA-SELENOCARBENIUM IONS FROM SE,O-HETEROACETALS AND THEIR REACTIONS, Journal of organic chemistry, 59(5), 1994, pp. 1011-1019
Various Se,O-heteroacetals were prepared by the LiAlH4 reduction of di
selenides 1 followed by alkylation with methoxymethyl chloride or (2-m
ethoxyethoxy)methyl (MEM) chloride. Olefinic and acetylenic alpha-sele
no carbenium ions were generated by the selective C-O bond cleavage of
O-(2-methoxyethyl)-Se,O-heteroacetals with titanium(IV) chloride and
cyclized to give the seleno heterocyclic compounds. Olefinic MEM-selen
ides 3a,b,d-f,h underwent the endo-mode cyclization to afford 4-chloro
selenacycloalkanes 4a,b,d-f,h in good yields, whereas acetylenic MEM-s
elenides 12b-e,g-j underwent the exo-mode cyclization to give 3-(1-chl
oroalkylidene)selenacycloalkanes 13b-e,g-j. This new utilization of al
pha-seleno carbenium ions was also applied to the intramolecular and i
ntermolecular Friedel-Crafts reactions.