Regioisomeric and Substituent Effects upon the Outcome of the Reaction of 1-Borodienes with Nitrosoarene Compounds

Abstract

(2015) 'Regioisomeric and substituent eects upon the outcome of the reaction of 1-borodienes with nitrosoarene compounds.', Journal of organic chemistry., 80 (13). pp. 6574-6583. Further information on publisher's website:http://dx.doi.org/10.1021/acs.joc.5b00593Publisher's copyright statement:This document is the Accepted Manuscript version of a Published Work that appeared in nal form in The Journal of Organic Chemistry, copyright c 2015 American Chemical Society after peer review and technical editing by the publisher. To access the nal edited and published work see http://dx.doi.org/10.1021/acs.joc.5b00593. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. with high regioselectivity in most of cases, in moderate to good yield. 1 H and 11 B NMR studies on two boro-oxazine regioisomers showed that selective deprotection can be performed.Formation of either the pyrrole or furan derivative is pH and regioisomer-structure dependent.The results obtained, together with previous B3LYP calculations, support mechanistic proposals which suggest that pyrrole, or furan formation, proceeds via oxazine formation, followed by a boryl rearrangement and an intramolecular addition-elimination sequence.

Towards the generalized iterative synthesis of small molecules

“…For example, many standard oxidations (Figure 5a), reductions (Figure 5b), and protecting group manipulations (Figure 5c) are well-tolerated. 145–151 Numerous other common synthetic transformations leave MIDA boronates intact, including aldol reactions, 145 carbonyl olefination reactions, 145 Mitsunobu reactions, 145 electrophilic substitution reactions, 149, 152 hydroborations and –stannylations, 151 Diels Alder cycloadditions (Figure 5j), 151, 153 and cyclopropanations. 147 A variety of transition metal-catalyzed reactions are also well-tolerated (Figure 5g), including Heck reactions, 147, 154 Grubbs metathesis, 147 Sonagashira couplings, 151 and Suzuki cross-couplings.…”

A Dienyl Boronate‐Aryl Nitroso Ene Reaction Entry to C‐Pyrrolyl Nitrones and Subsequent Conversion to Isoxazolidines

“…Overall, these experimental results suggest the following mechanistic rationale for the formation of nitrones 3 from 1 . The first step of this process could be the formation of a pyrrole 4 , as previously reported, followed by its conversion to nitrone. However, this hypothesis was readily excluded since pyrrole 4 a was recovered unchanged when it was brought into contact with excess of nitrosobenzene in EtOAc (see Scheme ).…”

“…We previously reported that 1‐boronated‐1,3‐dienes react with substituted nitrosobenzene in methanol to afford the resulting pyrroles 4 via a hetero‐Diels‐Alder, followed by ring contraction sequence (Scheme ) …”

Access to Fused Pyrroles from Cyclic 1,3-Dienyl Boronic Esters and Arylnitroso Compounds

“…To our knowledge, the only example of cyclic reactants described to date was reported by us, giving a low yield of pyrrole 8ba from 7b and nitrosobenzene 13a . Replacement of pinacol by diethanolamine (which causes quaternization of boron, making the diene more electron-rich, and thus increases the reactivity towards ArNO) had a beneficial effect as exemplified in Scheme …”

“…Indeed, some of these approaches have been applied to fused pyrroles . We recently proposed a new mild synthesis of N -aryl pyrroles from dienyl pinacol boronic esters and nitrosoarenes and, in this paper, we expand the scope of this methodology to the preparation of fused pyrroles 8 (Scheme ) and also include new metathesis reactions to access cyclic precursors 7 , which complements the classical routes usually employed for the synthesis of these valuable building blocks …”