3- pentyl propanethioate

Because anti/syn ratios in the product can be correlated to the E(0)/Z(0) ratio of the involved boron enolate mixture,10b initial experiments were aimed at the preparation of highly E(0)-enriched boron enolate. The E(0)/Z(0) ratio increases with the bulk of the alkanethiol moiety, whereas the formation of Z(O) enolates prevails with (S )-aryl thioates. (E/Z = 7 93 for benzenethiol and 5 95 for 2-naphthalene thiol esters). E(O) reagent can be formed almost exclusively by reaction of (5)-3,3-diethyl-3-pentyl propanethioate 64 with the chiral boron triflate. High reactivity toward aldehydes can be retained in spite of the apparent steric demand (Scheme 3-22).43... 

Asymmetric aldol reactions.1 The reagent 3, prepared by reaction of (S)-3-(3-ethyl)pentyl propanethioate (2) and ethyldiisopropylamine with (S,S)-2,5-di-... 

The (0)-reagent (91) is formed almost exclusively from S-3-(3-ethyl)pentyl propanethioate (92) and borolanyl triflate (90). Despite its apparent steric demand, (91) still retains a high degree of reactivity towards aldehydes (in Scheme 21 the interaction between R and Me is not exceedingly large). Summarized in Table 6 are the results obtained from aldol reactions of representative aldehydes with (91 Scheme 38). All reactions proceed smoothly at -78 °C and the major products have the 2,3-anti stereochemistry (antiisyn > 30 1). With (2 ,55)-(90) the aldehydes examined provide, in most cases, the (2R) aldol products with more than 98% ee. It is important to note that the external chiral moiety can be recovered as its 2,2-dimethylaminoethanol complex, and that the aldol products are equipped with a versatile thioate functionality for further synthetic transformation. 

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See also in sourсe #XX -- [ ]

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