(1R,5S,6R)-3-(tert-butoxycarbonyl)-3-azabicyclo[3.1.0]hexane-6-carboxylic acid

Numerous reports have been published both domestically and internationally on the synthesis of 3-azabicyclo[3.1.0]hexane. 3-azabicyclo[3.1.0]hexane mainly consists of two parts: a five-membered azabicyclohexane and a three-membered ring. Therefore, the preparation process inevitably involves the construction of the five-membered and three-membered rings. The five-membered ring is often constructed based on cis-1,2-disubstituted cyclopropane; the three-membered ring is usually formed by the reaction of a conjugated five-membered ring with carbene or thioylide. The synthesis of (1R,5S,6R)-3-(tert-butoxycarbonyl)-3-azabicyclo[3.1.0]hexane-6-carboxylic acid uses relatively inexpensive diethyl fumarate and ethyl chloroacetate as starting materials. A cyclopropane structure is constructed via a Michael addition reaction under base catalysis. The reported yield reached 80%, with subsequent reaction conditions being relatively mild and yields consistently high. In the preparation of I-3, according to the literature, the amide bond can be selectively reduced while the ester group is retained when both the ester group and the amide bond are present. The yield is as high as 90%. The yield of the first step of the entire route is only 80%, and the yields of the other steps are all above 85%, which meets the requirements of large-scale industrial production [1]. The preparation route is as follows:

[1] Patent: US2014/343295, 2014, A1. Location in patent: Paragraph 0087; 0088; 0089
[2] Bioorganic and Medicinal Chemistry Letters, 2014, vol. 24, # 4, p. 1067 - 1070