Carbamate-protected primary amines, synthesis

The procedure has been extended to the synthesis of 7V,7V -substituted diamines 166 from the diazides 164 and dichloroboranes 165177. Primary amines protected by the t-butoxycarbonyl group are obtained by the action of trialkylboranes R3B (R = Bu, s-Bu, CsHn or cyclohexyl) on the lithium or potassium salt of t-butyl 7V-(tosyloxy)carbamate (equation 62)178. 

Nitro-l/f-p5rrazole-l-[A/, 7V-bis(tert-butoxycarbonyl)]carboxamidine (1) has been developed as a new reagent for the rapid and efficient solid and solution phase synthesis of bis(carbamate)-protected guanidines from primary and secondary amines <99TL53>. 

In a synthesis of 4-hydroxypipecolic acid, Varela and co-workers protected the primary amine unit in 147 as the benzyl carbamate (148).Manipulation of the protected diol led to the primary mesylate in 149, and catalytic hydrogenation removed the Cbz group to give the primary amine in 150. 

A similar approach was reported by Wang a year later, involving a double Michael reaction of oxindoles with dienones [31]. A cinchona-based primary amine catalyst catalyzed the reaction, and good yields and excellent enantioselectivities were obtained when diaryldienones were used. The only requirement for the reaction was the use of the carbamate-protected oxindoles thus, the use of unprotected or benzy-lated oxindoles is ineffective for this synthesis. 

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