Stereoselective Hydrostannation of Diacrylate and Dimethacrylate Esters of Galactaric Acid Derivatives: Cyclohydrostannation vs. Diaddition？

This paper reports a study on the free radical hydrostannation of ((4 S,4′ R,5 R,5′ S)-2,2,2′,2′-tetramethyl-[4,4′-bi(1,3-dioxolane)]-5,5′-diyl)bis(diphenyl methylene) diacrylate ( 1) and dimethacrylate ( 2) with triorganotin hydrides, R 3SnH (R = Me, n-Bu, Ph). Preliminary investigations show that these reactions could lead to mixtures of products of cyclohydrostannation and/or mono- or diaddition according to the organotin hydrides employed and the reaction conditions used. The addition of Me 3SnH to 1 afforded a mixture of three organotin compounds from which the pure new 13-membered macrodiolide 3 (48%) was obtained. The other two organotins could not be separated. The addition of n-Bu 3SnH to diester 1 led to a mixture of two organotins, the one in major proportion (91%) being the product of diaddition 7. The minor product 6a (9%) could not be isolated pure. The hydrostannation of 1 with Ph 3SnH led to one organotin: The product of diaddition 8. The hydrostannation of the dimethacrylate 2 with the organotin hydrides R 3SnH (R = Me, n-Bu, Ph) under the same reaction conditions, led in the three cases to mixtures containing mainly diaddition products, and no cyclization products were detected. Some physical characteristics of the new compounds including selected values of 1H, 13C, and 119Sn NMRs are included