David A. Johnson, G. Gribble
Nov 2, 2018
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Journal
Organic Preparations and Procedures International
Abstract
In connection with a project in our laboratory we required an efficient, safe, and scalable synthesis of 3-butenylamine (4-amino-1-butene) (1). Although such homoallylic amines are well known, syntheses of the parent 3-butenylamine are sparse. Galand reported the hydrogenation of allyl cyanide with zinc-copper couple to give 1 in unspecified yield. Roberts described a three-step sequence to give 1 via benzenesulfonation of 3-butenyl alcohol (allylcarbinol), displacement of benzenesulfonate with azide ion, and reduction of the azide with lithium aluminum hydride to give 1 in 61.5% from the benzenesulfonate. Both Roberts and later Brown noted that lithium aluminum hydride reduction of 3-butenonitrile (allyl cyanide) was unsatisfactory, perhaps due to the acidity of the a-hydrogens of the nitrile. Brown nicely circumvented this obstacle by employing the less basic aluminum hydride, and was able to reduce 3-butenonitrile to 1 in 55% yield. However, we were only able to obtain 1 in 8–12% yield using aluminum hydride. Courtois reported the synthesis of 1 in 40% yield via the reaction of allyl aluminum bromide with (methoxymethyl)-N,N-bis(trimethylsilyl) amine. Contrary to these reduction protocols for accessing 1, we envisaged a direct amination strategy making use of the venerable Gabriel amine synthesis in combination with a Mitsunobu reaction. Our successful synthesis of 1 using this methodology is shown in Scheme 1. Thus, reaction of commercially available 3-butenyl alcohol (2) with phthalimide (3), triphenylphosphine, and diethyl azodicarboxylate (DEAD) gave the expected phthalimide 4 in 85% yield. Cleavage of 4 with hydrazine yielded 3-butenylamine (1) in 54% yield following distillation. In conclusion, we report a simple, convenient, and potentially scalable preparation of 3-butenylamine in two steps that avoids the use of air-sensitive hydride and aluminum reagents and possibly explosive azide intermediates.