Synthesis of 1,4-diaza-7-oxabicyclo[4.3.0]non-2-en-6-ones by cyclization of 1,1-bis(trimethylsiloxy)ketene acetals with pyrazine and quinoxaline

Synthesis of azoxabicyclo[3.3.1]nonanones based on diastereoselective reactions of 1,1-bis(trimethylsilyloxy)ketene acetals with isoquinolines and quinolines

“…The structure of all products was established by spectroscopic methods. The 1 H and 13 C NMR spectra of compounds 3 and 4 are largely dominated by the hindered rotation about the N-CO bond of the carbamate moiety which gives rise to the existence of two rotamers: I (major) and II (minor) (Scheme 1). Hence, 13 C correlation spectra (HSQC, HETCOR, HMBC).…”

“…12b Cyclizations of 1,1-bis(trimethylsiloxy)ketene acetals with pyrazine and quinoxaline were reported by Rudler 12b and by us. 13 The cyclizations of 1,3-bis(trimethylsilyloxy)-1,3dienes (masked 1,3-dicarbonyl dianions) 14 with isoquinoline, 15 quinoxaline, 16 and quinazoline 17 provide a convenient approach to various bridged N-heterocycles. Recently, we reported the synthesis of 7,8-benzo-9-aza-4-oxabicyclo[3.3.1]nonan-3-ones based on the cyclocondensation of isoquinolinium salts with 1,1bis(trimethylsiloxy)ketene acetals.…”

Cyclization Reactions of 1,1-Bis(trimethylsilyloxy)ketene Acetals

“…The reaction of pyrazine (52) with bis(silyloxy)ketene acetals, such as 51, afforded various 1,4-diaza-7-oxabicyclo[4.3.0]non-2-en-6-ones, such as 53, as separable mixtures of diastereomers (Scheme 16). 40,41 The reaction of quinoxaline (54) with 46 afforded 2,3benzo-1,4-diaza-7-oxabicyclo[4.3.0]non-2-en-6-one 55 as a separable mixture of diastereomers (Scheme 17). 40,41 The lactone and the quinoxaline system were annulated with cis-configuration.…”

“…40,41 The reaction of quinoxaline (54) with 46 afforded 2,3benzo-1,4-diaza-7-oxabicyclo[4.3.0]non-2-en-6-one 55 as a separable mixture of diastereomers (Scheme 17). 40,41 The lactone and the quinoxaline system were annulated with cis-configuration. A number of related products were successfully prepared.…”

Synthesis of Bridged and Nonbridged N‐Heterocycles by Cyclocondensation of Bis(silyl enol ethers) with Iminium Salts

“…The reaction of 1,1‐bis(trimethylsiloxy)ketene acetals 7 with pyrazine ( 15 ) and quinoxaline ( 16a ) mediated by methyl chloroformate afforded 1,4‐diaza‐7‐oxabicyclo[4.3.0]non‐2‐en‐6‐ones 17 (Scheme ) 16,21,22. The formation of these products can be explained by generation of an iminium ion, attack of 7 , generation of a second iminium ion, and subsequent cyclization.…”