Die Gasphasen‐Flussthermolyse von 1‐Isobutenyl‐ und 2‐Methylphenyl‐alkinyl‐ketonen. Eine Synthese von Methylenomycin B

Abstract

The Gas‐Flow Thermolysis of 1‐Isobutenyl Alkynyl and 2‐Methylphenyl Alkynyl Ketones. Synthesis of Methylenomycin B The gas‐flow thermolysis of 1‐isobutenyl alkynyl or 2‐methylphenyl alkynyl ketones were found to lead to phenols and cyclopentenones or to naphthols and indanones, respectively. These conversions involve two cyclization processes so far unknown with α‐alkynones; they are interpreted as intramolecular additions of an allylic or a benzylic C,H bond to a triple bond which may occur in two directions. In addition, the cyclopentenones formed by the α‐alkynone cyclization, a known carbene process yielding 5‐rings, were also found. The available evidence ruled out a carbene process yielding 6‐rings. The addition process yielding 5‐rings was applied to a short (but low yield) synthesis of methylenomycin B .