Sunzvnary Stereoselective total synthesis of ( *)-trimethylsequirin-B (16) and the formation ( -J-)-trimethylsequirin-C (14) in an intermediate stage is described.

SL1 4AUCyclisations of 2-phenylethyl isocyanate (2), ( + ) -I -methyl-2-phenylethyI isocyanate (3). and 2,2-diphenylethyl isocyanate (4) have been studied using polyphosphoric acid, aluminium chloride, boron trifluoride-diethyl ether, and triethyloxonium tetrafluoroborate. Depending on the reaction conditions, triethyloxonium tetrafluoroborate, forexample, notonlygavetheexpected isoquinolones (1 4)-(I 6) and other expected products, but in two cases, also gavethe2-N-(2-phenylethyl)formamidyl-3,4-dihydroisoquinolin-l (2H)-ones ( 9) and (1 0). Theisoquinolone (1 5) w a s alkylated with triethyloxonium tetrafluoroborate or methyl fluorosulphonate to give 1 -ethoxy-( 7) or 1met h oxy -3 -met h y I -3,4 -d i hydro i soq u i no I in e ( 8), respective I y . INTRAMOLECULAR cyclisation of isothiocyanates providesa useful synthesis of isoquinolines,l thienopyridines,2 ben~azepines,~ and thieno[3,2-~]azepines.~ Thus, for example, cyclisation of 2-phenylethyl isothiocyanate with triet hyloxonium tetrafluoroborate gives 1 -ethylthio-3,4-dihydroisoquinoline (5) .l These results prompted us to study cyclisations of the corresponding isocyanates with triethyloxonium tetrafluoroborate and other reagents.At the start of our work 6,7-diniethoxy-3,4-dihydroisoquinolin-1 ( 2 H ) -one (corydaldine) had been synthesised by cyclisation of homoveratryl isocyanate with phosphoryl chloride and polyphosphoric acid while the latter reagent had been used also to synthesise other 3,4dihydroisoquinolin-1 (2H)-ones.6 Since then, polyphosplioric acid and boron trifluoride-diethyl ether * have been used successfully to cyclise p-arylethyl isocyanates. A recently reported two-stage treatment with phosphorus oxychloride and tin(rv) chloride appears to be

With triethyloxonium tetrafluoroborate or ethyl or methyl fluorosulphonate, 2-arylethyl isothiocyanates cyclised to give a 1 -ethylthio-or 1 -methylthio-3,4-dihydroisoquinoline, respectively. These compounds were prepared also by successive cyclisation of the isothiocyanates with aluminium chloride or polyphosphoric acid and alkylation of the resultant 3,4-dihydroisoquinoline-? (2H) -thione. They are useful starting materials for the synthesis of other 1 -substituted 3,4-dihydroisoquinolines, e.g. 1 -amino-compounds.?At approximately the time our first patent application 2 was published another appeared in which compounds (12), ( 14), and the hydroiodide of compound (1 7) are described along with several l-amino-3,4-dihydroisoquinolines [C.

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