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A new method for cyclodehydration of o-hydroxyaryl-β-ketols to 4-chromanones using HMPT is described. The method has general applicability. It is particularly useful for the cyclisation of labile intermediates as exemplified by the synthesis of cannabinoid synthon, 2-methyl-2-(4-methyl-3-pentenyl)-7-methoxy-4-chromanone.

2-Hydroxy-4, 6-dimethoxycrotonophenone (1), isolated from the plant Dysophylla stellata Benth. by Joshi and Ravindranath,1 is the only example of an open chain form of chromanones. The co-occurrence of the crotonophenone (1) with chromone and butyrophenone1 suggests that these are biogenetically related in the same way as chalcones are to flavonoids.2 It is likely that more crotono-phenones and 2-methylchromanones will be discovered in nature.

Mevalonic acid lactone (MVA) labelled with stable as we11 as radioactive isotopes continuesto be one of the most widely used substrates in the biosynthesis of terpenoids. Elucidation of several intricate biochemical processes has been possible through the use of carefully chosen specifically 1abelled MVA.1 Attempts to develop new routes to its synthesis have, therefore, been continued and several elegant syntheses have been reported in recent years.2 Wedescribe here a short and efficient synthesis of MVA in which condensation between butan-1-01-3-one (2a) and acetic acid is brought about through their trimethylsilyl (TMS) derivative.3 Usual acidic work up of the reaction brings about cleavage of TMS groups thus obviating deprotection step used in most of the other syntheses.