Pyridine-phosgene adduct

Pyridine-phosgene adduct l-[2-(Chloroformyl) -2-azacyclohexa-3,5-dienyl] pyridinium chloride (2-DHPP)... 

The originally proposed 1 2 structure (II) for the phosgene-pyridine adduct was deduced by analogy to the commonly observed 1 1 pyridinium salt (I) as shown in scheme 118. However, as a conclusion of a study of low temperature NMR and solid-state CP/MAS spectra, King Jr. and coworkers (Ref. 170) assigned a dihydropyridine-pyridinium (2-DHPP) structure (III) to the 1 2 salt. 

Addition of hydrogen sulfide (0.5 molar equivalent) to cyclopropanone in dichloromethane afforded the bis-adduct 1, which could be spirocyclized with excess phosgene in the presence of pyridine to give 8,10-dioxa-4-thiadispiro[2.1.2.3]decan-9-one (2). Thermolysis of this cyclic carbonate at 495°C in vacuo (0.5 Torr) yielded methylenethiirane 3, an elusive species in the methyleneheteracyclopropane series. 

Treatment MBH adducts with aluminium trichloride (from the acetate), thionyl chloride,phosgene and A-chlorosuccinimide (NCS)/dimethyl sulflde, respectively, furnishes chlorides 65 and 66. With thionyl chloride in the presence of pyridine, the MBH adduct gives predominantly the unrearranged chloride 66. Equimolar mixtures of rearranged and unrearranged chlorides were obtained from ethyl 2-(l-hydroxyethyl)acrylate and ethyl 2-(l-hydroxybutyl)acrylate with hexachloroacetone/triphenylphosphine, while... 

In the above procedure, the reactive species is an ionic adduct of pyridine and phosgene and reaction occurs as follows ... 

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