CONTENTS  INTRODUCTION  REACTION  MECHANISM  APPLICATION  SCOPE  CONCLUSION  REFERENCE

INTRODUCTION  First observed by Henry Gilman in early Suggested the migration of the Si group.  Extensively developed in 1957 by Adrian G. Brook - Proposed a nucleophilic attack of oxygen to α-silicon atom.

INTRODUCTION

DEFINITION  The 1,2- migration of a silyl group from carbon to oxygen under basic conditions is known as Brook rearrangement.  Rearrangement of α- silyl oxyanion to α-silyl carbanions involving a penta coordinate silicon intermediate.

Amines Sodium hydroxide Organolithi um reagent Alkali metal alloy BASE

METHODS GENERATION OF α -SILYL ALKOXIDES:

METHOD 1:  Reaction of acylsilanes with a nucleophile METHOD 2:  Although deprotonation of the corresponding α-silyl alcohols METHOD 3:  Addition of silyl metallic reagents to aldehydes or ketones

DRAWBACK:  Organosilyl metal reagents are only readily generated when there is atleast one anion stabilizing group such as phenyl attached to the silicon. METHOD 4:  Regioselective β-ring opening of α,β- epoxysilanes can also same as a source of α-silyl alkoxides.

CHARACTERISTICS

OUTLINE OF REARRANGEMENT MECHANISM:

MECHANISM-STEPS INVOLVED  The mechanism as described by Brook includes the formation of a cyclic pentavalent silicon species.  Immediately following the deprotonation.  Subsequent ring opening and irreversible.  Fast protonation of the carbanion by the starting alcohol or the conjugate base leads to the corresponding silyl ether.

MECHANISM OF REACTION

SYNTHETIC APPLICATIONS APPLICATION 1:  K. Takeda and co-workers synthesized the tricyclic core of the cyanthins using a Brook rearragement reaction.

APPLICATION 2  K. Takeda developed a new synthetic strategy for the stereoselective construction of 8 membered carbocycles utilizing a Brook rearrangement.

APPLICATION 3  E.J. Corey synthesized (+)- Onocerin from farnesyl acetate- derived acyl silane via four-component coupling and tetracyclization steps.

APPLICATION 4  Brook rearrangement is used for another important name reaction called vinylogues Michael-cascade reaction.(vinylation and 1,2-brook rearrangement reaction is used).

APPLICATION 5  It is used in the synthesis of alpha hydroxyl acid derivatives are important in the cosmetic industry.

APPLICATION 6  1,4 Brook rearrangement – wittingreaction-synthesis of silyl dienol ether.

APPLICATION 7  For the preparation of functionalised,stereo defined 8- membered ring. APPLICATION 8  Silyl ethers are used as protecting agents for alcohols.

APPLICATION 9  Synthesis of gamma amino β- hydroxy amines(lactum synthesis).

APPLICATION 10  Useful in tandem with other reactions via the addition of electrophile.

SCOPE  Brook rearrangements are known in acylsilanes. Beyond that, acylsilanes are well known for their hydrolysis in basic solution to a silanol and an aldehyde – initiated by attack-carbonyl group.acylsilanessilanolaldehyde  A related reaction, involving initial attack at the silicon center, causes migration of one of the silicon groups to the carbonyl carbon, which initiates a Brook-Rearrangement. If the silicon group was chiral, the end product is a chiral silyl ether, as the migration occurs stereo specifically.stereo specifically

Conclusion  The Brook rearrangement has been applied widely since its discovery in  Brook Rearrangement makes silyl enol ethers  Useful reaction in tandem with others to form bonds  Several one-pot synthesis in recent literature  Recent literature have used this chemistry to synthesize the following 1. γ-amino-β- hydroxy amide 2. α- hydroxy acid derivatives 3. Aryl vinyl ketones 4. Eight-membered rings 5. Silyl dienol ethers

REFERENCE 1.Jie Jack Li:Name Reactions Third Edition;Springer Science & Bussiness Media, 2006:Page no: Brook, A. G. (1958). "Isomerism of some α- hydroxysilanes to silyl ethers". J. Am. Chem. Soc. 80: 1886– Laszlo Kurti,Barbara Czako:Strategic Applications of Named Reactions in Organic Synthesis;Elsevier,29-Apr-2005;page no: Christian M. Rojas:Molecular Rearrangements in Organic Synthesis:Wiley,March-2015,Page no:

5.A. Hassner, I.Namboothiri;Organic Syntheses Based on Named Reactions, Third Edition;Elsevier;Page no:62 6. : Boyce, Gregory R. and Johnson, Jeffery S., J. Org. Chem. 2016, 81,