Ferf-Butyl isocyanide

Krasavin et al. described the synthesis of dihydropyrazol pyrazine diones via Ugi-4CR, employing ferf-butyl isocyanide as a convertible reagent [102], The authors reported that, under microwave irradiation, the ferf-butyl isocyanide behaves similar to Armstrong s isocyanide, furnishing the DKPs in good yields. It is noteworthy that the low priced isonitrile applied may be helpful for developing large-scale syntheses in the future (Scheme 6). 

Double silylation is also observed in the reaction of a,/3-unsaturated ketones with a bis(disilanyl)dithiane, resulting in high yields of cyclic silyl enol ethers [Eq. (65)].58 The catalyst for this reaction is a cyclic bis(silyl)pal-ladium(II) bis(ferf-butyl isocyanide) complex. Analogous reactions of ester... 

The present procedure is the best way of preparing aliphatic isocyanides boiling above ethyl isocyanide. It has been applied to the synthesis of the following isocyanides 6 isopropyl (38%), -butyl (61%), tert-butyl (68%), and benzyl (56%). In preparing isopropyl isocyanide or ferf-butyl isocyanide, the petroleum ether should be of boiling point 30-35°, as otherwise it is difficult to separate these low-boiling isocyanides in the indicated yield, and,... 

Wessjohann and coworkers reported in 2008, a concise synthesis of cyclic RGD pentapeptoids by three consecutive Ugi-4CR including one for macrocyclization [63]. Thus, reaction of 23, obtained from 22 in two steps, with formaldehyde and ferf-butyl isocyanide in methanol afforded, after global deprotection under acidic conditions, the pentapeptoid 24 in 33% yield in four steps (Scheme 9). 

Indeed, this MCR worked extremely well by simply stirring the three components in trifluoroethanol (TFE) at room temperature. Interestingly, no high-dilution conditions were required for the above transformation. Authors prepared 12-, 15-and 18-membered macrocycles and even nine-membered medium-sized cycles in excellent yields with diastereoselectivities. Two examples were depicted in Scheme 11. Thus, stirring a TFE solution of aziridine aldehyde 29, dipeptide 30 and ferf-butyl isocyanide at room temperature for 4 h afforded a nine-membered cycle 31 in 83% yield. Similarly, a 18-membered cyclopeptide 33 was obtained in 77% yield by the reaction of 29, pentapeptide 32 and ferf-butyl isocyanide. In both examples, the cyclic compounds 31 and 33 were formed with high diastereoselectivities (dr > 20/1). This is intriguing, as Ugi reaction provided generally low to moderate stereoselection when chiral substrates was used as inputs ([66-72] for enantioselective isocyanide-based MCRs, see [73-80]). 

It is well documented that carbenium ions undergo nucleophilic attack by the carbon atom of isocyanides [46]. Significantly, diphosphirenium 2 Pa reacts at -50°C with ferf-butyl isocyanide in a similar manner to give the transient ni-trilium salt 21, which undergoes a ring expansion reaction affording 22 [45] (Scheme 16). Note that 22 is one of the very rare four-membered heterocycles featuring a phosphaalkene moieties [47]. 

Huige and Hezemans179 180 have performed extensive molecular mechanics calculations using the consistent force-field method on various oligo- and polyisocyanides. The hexadecamer of ferf-butyl isocyanide was calculated to have a helical middle section and disordered ends. The dihedral angle N=C—C=N in the middle section was found to be 78.6°, and the number of repeat units per helical turn was 3.75. The latter number is in agreement with circular dichroism calculations using Tinoco s exciton theory (3.6—4.6) and De Voe s polarizability theory (3.81). The molecular mechanics calculations further predicted that the less bulky polymers 56 and 57 form helical polymers as well, whereas a disordered structure was calculated for poly(methyl isocyanide) (55). 

In this review, monoisocyanide polymers are denoted as poly(isocya-nide)s rather than using the systematic name, poly(iminomethylene)s , because the former name is more familiar to non-experts in this area. For example, poly(N- terf-butyliminomethylene) is denoted as poly( ferf-butyl isocyanide). On the other hand, the systematic name poly(quinoxaline-2,3-diyl) is used for polymers of 1,2-diisocyanobenzene to differentiate the fact that the polymerization process is accompanied by the formation of quinoxaline rings. 

Among the polymerizations of tert-butyl isocyanide using a series of optically active amines, 1-phenylethylamine (47) served as the most stereoselective initiator, leading to the formation of optically active poly(ferf-butyl isocyanide) with a 61-62% screw-sense excess (Scheme 36) [59]. A P-helical... 

Addition of EtMgCl to a mixture of ZZbMCQ and ferf-butyl isocyanide in hexane afforded 22bMCl-(EtC=N-f-Bu) in 64% (Zr) and 51% (Hf) yield (Scheme... 

Phenyl- -alanine, cyclohexanone, and ferf-butyl isocyanide in methanol stirred 72 hrs. at 20° -> l-(2-0x0 -4- phenyl -1- azetidinyl) -1- cyclo-hexanecarboxylic acid ferf-butyl-amide. Y ... 

A related cyclization of p-ketoketimines 117, obtained by reaction of ferf-butyl isocyanide with 4-aryl-l,l,l-triflnorobutan-2,4-diones 116, afforded 2,3-diamino-4-aroyl-5-(trifluoromethyl)furans 118 [91],... 

A soln. of 1-bromo-l-N-ferf-butylcarboxamidocyclohexane in abs. ether stirred 1 hr. at —15° with K-ferf-butoxide, and the crude intermediate heated 10 min. at 75° with stirring ferf-butyl isocyanide (Y 63%) and cyclohexanone (Y ... 

Hf(S2CNEt2)4] has been prepared from the analogous hafnium ferf-butyl isocyanide complex (615). 

In the first in a new series of papers the synthesis and characterisation of Cr(II) carbonyl and ferf-butyl isocyanide complexes, such as the structure shown as 24, have been reported. Again the synthesis and characterisation of the di-alkyl(butadiene)cyclopentadienylmolybdenum(III) complexes, such as the complex shown as 25, have been prepared in the reactions of the CpMo(ri -diene)Cl2 (diene = 1,3-butadiene, isoprene, CsHg 2,3-dimethyl-1,3-butadiene, CeHio)... 

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