Some conversions of allenyl ethers

Metallation of methoxypropadiene, CH2 = C = CHOCH3, with butyllithium in ether, followed by reaction with carbonyl compounds, R1R2C = O (R1 and R2 = H or alkyl or R1R2C = cyclohexyl), affords carbinols, CH2 = C = C[CR1R2 (OH)]OCH3, in excellent yields. Acid-catalysed hydrolysis of these carbinols gives nearly quantitative yields of unsaturated ketols, 1-Methoxy-1-methylthiopropadiene, CH2 = C = C(OCH3) (SCH3) (VI), has been obtained in 75% yield by adding CH3SSCH3 to the lithiated allenyl ether. Acid-catalysed addition of alcohols, ROH (R = CH3 or C2H5), to methoxypropadiene affords acrolein acetals, CH2 = CHCH(OCH3) (OR) (VII), in good yields. Diels-Alder addition of ethoxypropadiene to a,β-unsaturated aldehydes, R3CH = CH - CH = O (R3 = H or CH3), leads to derivatives of 2,3-dihydropyran (VIII). The yields are moderate.