ABSTRACT
The first synthesis of phosphonoacrolein 3 was made in quantitative yield by acidic treatment of beta-ethoxy-alpha-(methoxymethyl)vinylphosphonate 2, derived from a beta-ethoxy-alpha-phosphonovinyl anion and MOMCl. The phosphonoacrolein 3 easily underwent a hetero-Diels-Alder reaction with electron-rich alkenes 4a-f or alkynes 9a-c under mild conditions, and phosphono-substituted pyrans 5a-d, 6e,f or pyranopyrans 11a-c were obtained in good to excellent yields. The reaction of 3 with cyclopentadiene and cyclohexadiene led to mixtures of [2 + 4] and [4 + 2] cycloadducts 7a, 8a and 7b, 8b in modest yields. The cycloaddition reaction between 3 and pyranopyran 13 or dibromocarbene and 13 resulted in [4 + 2] or [2 + 1] cycloadducts 14 or 15 in good yields.
ABSTRACT
The beta-hetero-substituted vinylphosphonates 1a-c on treatment with LDA or LTMP were readily lithiated at the alpha-position of the phosphono group, and the resulting alpha-lithiovinylphosphonates were trapped with various electrophiles to afford the corresponding alpha-functionalized vinylphosphonates 2-14 in 55-96% yields. The Friedel-Crafts reaction of alpha-(silyl)- or alpha-(germyl)phosphonoketene dithioacetals 2, 9, or 4 with acid chlorides gave alpha-acylated phosphonoketene dithioacetals 15-19 in 53-91% yields. The palladium-catalyzed cross-coupling reaction of beta-ethoxy-alpha-(tributylstannyl)vinylphosphonate 13 with a variety of organic halides (R = acyl, allyl, aryl, etc.) provided beta-ethoxy-alpha-substituted vinylphosphonates 21-26 in good to moderate yields. The palladium-mediated cross-coupling reaction of alpha-(iodo)vinylphosphonates 7 and 14 with terminal acetylenes afforded alpha-alkynylated vinylphosphonates 41-44 in 69-83% yields. Several alpha-functionalized beta-hetero-substituted vinylphosphonates were applied to the synthesis of pyrazoles and an isoxazole possessing a phosphono function.
