Carbene Analog Insertions

The transition metal-catalyzed C-H insertion reaction of carbenes to organic compounds is a well-established synthetic method, as shown in the first two sections in this chapter. However, nitrene C-H insertion, the corresponding reaction of carbene analog, is much less known. In the past decade, considerable advances have been made in the development of this chemistry into a generally useful C-H amination process by using improved catalysts and protocols, in which readily available amines or amides are used as the starting substrates. Moreover,... 

Insertion of highly reactive group 14 carbene analogs into metal-metal bonds is a step toward cluster building and germylenes readily insert into the Fe—Fe bond of [CpFe(CO)2]2 under mild conditions (equation 20)101. 

Insertion of isocyanides into the Mn—N bond of bis(iminoacyl) complexes (35) gave the aza-manganacycles (36) as major products (Equation (1)) <890M2589>. X-ray studies suggest that these species are carbene complexes (as shown in (36)) rather than true heterocycles. Analogous insertion of isocyanides into the Pt—C bond has led to Pt-S metallacycles <90JCS(D)78i > (see Section 3.20.9.5) and into the Ir—N or Ir—O bonds has afforded Ir-N or Ir-O heterocycles <88JA3704> (see Section... 

A second route was devised using chiral /3-keto ester 14, which was identified as our precursor for 2 [7]. This idea was in analogy with the carbapenem chemistry [8], as depicted in Scheme 2.4, where Masamune reaction [9] for carbon elongation, diazo-transfer, and transition metal-mediated carbene insertion reaction [10] were employed as key steps sequentially. 

Divalent compounds of group 14 metals, i.e., heavier analogs of carbenes, are highly reactive and readily insert into various bonds. Therefore, these species are useful for the formation of M-E (M = Si, Ge, Sn E = S, Se, Te) bonds. 

It is suggested that the real carbene, generated by thermolysis of the diazo or diazirine precursors or photolysis of 40, gives mostly 1,3-insertion, whereas photolysis of either the diazoalkane or diazirine yields much 1,2-Me migration directly from precursor excited states.15 1 An analogous intervention of 1,2-Me migration via RIES was also observed in the photolytic decomposition of f-butylchlorodiazirine (24) to f-butylchlorocarbene (18) cf. Eq. 14.27... 

By analogy with the intramolecular insertion of phenylthiocarbenes, the reaction of (oo-oxido)diazoalkanes 93 resulted in the formation of cycloalkenes 94.38 However, the reaction was proven to proceed not via a carbene route b but a nitrene route a as shown in Scheme 26. The nitrene route is supported by the formation of heterocyclic products 98 and 99.39 This insertion reaction was used in the cydization step to the cyclopentene ring formation of isocarbacycline 97.40... 

The utilization of the dibromides 315 permitted the generation of 311 by MeLi. Since MeLi is less reactive as a nucleophile than wBuLi, the ring opening of 311 by addition of the methyl anion analogous to the formation of 314 (Scheme 6.67) was of no importance. However, in the case of 315 (R = CH2Ph), the intramolecular insertion of the transient carbenoid or carbene, leading to 312, was the main reaction and hence the cause of low yields of the respective cycloadducts 316, 317, 319 and 320. Whether such an insertion has to be blamed for the very modest yields of 316 and 317 with R= Me could not be proved [154]. 

By analogy with the mechanism proposed for the reaction with alkenes, C—H insertion product formation can be explained in terms of a H abstraction-recombination process of triplet arylcarbenes. The observations that ground-state singlet carbenes, for example, chlorophenylcarbene (67), produce only O—H insertion... 

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