Exhibit 5.1

Loeb & Loeb LLP   345 Park Avenue New York, NY 10154

Main   212.407.4000 Fax      212.656.1307

June 10, 2026

D. Boral ARC Merger Corporation

10 East 53rd Street, Suite 3001

New York, NY 10022

Ladies and Gentlemen:

We have acted as United States securities counsel to D. Boral ARC Merger Corporation, a Delaware Corporation (the “Company”), in connection with the Registration Statement on Form S-4 (File No. 333-295869) initially filed by the Company with the Securities and Exchange Commission (the “Commission”) on May 14, 2026 under the Securities Act of 1933, as amended (the “Act”). Such Registration Statement as amended, or supplemented, is hereinafter referred to as the “Registration Statement”. The Company has entered into a Business Combination Agreement, dated as of January 11, 2026 (the “Business Combination Agreement”) by and among the Company, D. Boral ARC Acquisition I Corp., a British Virgin Islands business company and the parent of the Company (“Parent”), D. Boral Arc Merger Sub Inc., a Delaware corporation and wholly-owned subsidiary of Parent (“Merger Sub”), and Exascale Labs Inc., a Delaware corporation (“Exascale”). Pursuant to the Business Combination Agreement, Merger Sub will merge with and into Exascale, with Exascale continuing as the surviving entity and as a wholly-owned subsidiary of the Company (the “Merger”). Prior to the effective time of the Merger (the “Effective Time”), the Company will merge with and into Parent with the Company continuing as the surviving entity in order to change from an exempted company in the Cayman Islands to a corporation incorporated under the laws of the State of Delaware (the “Domestication Merger”). The Domestication Merger is subject to the approval of the shareholders of the Parent.

On the effective date of the Domestication Merger, among other things, (i) all of the currently issued and outstanding ordinary shares, par value $0.0001 per share, of Parent (the “Ordinary Shares”) will convert automatically by operation of law, on a one-for-one basis, into shares of Class A Ordinary Common Stock, par value $0.0001 per share, of the Company (the “Class A Ordinary Common Stock”), and (ii) each of Parent’s currently issued and outstanding warrants (the “Warrants”), issued pursuant to that certain Warrant Agreement, dated as of July 30, 2025, by and between Parent and Odyssey Transfer and Trust Company (the “Warrant Agreement”), will automatically become, pursuant to Section 4.5 of the Warrant Agreement, warrants to acquire shares of Class A Ordinary Common Stock (the “Company Warrants”).

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This opinion is being rendered in connection with the registration under the above-referenced Registration Statement of (i) 41,200,000 shares of Class A Ordinary Common Stock issuable upon conversion of the outstanding Class A Ordinary Shares and Class B Ordinary Shares of Parent into shares of Class A Ordinary Common Stock (the “Conversion Shares”), (ii) 19,256,000 shares of Class A Ordinary Common Stock issued as consideration to certain holders of issued and outstanding shares of common stock of Exascale pursuant to the Business Combination Agreement the “Exascale Class A Shares”), (iii) 30,744,000 shares of Class B Super Common Stock, par value $0.0001 per share, issuable as consideration to certain holders of the issued and outstanding shares of common stock of Exascale pursuant to the Business Combination Agreement (the “Exascale Class B Shares”), and (iv) 14,100,000 Company Warrants to purchase 14,100,000 shares of Class A Ordinary Common Stock (the “Company Warrants”).

We have examined such documents and considered such legal matters as we have deemed necessary and relevant as the basis for the opinions set forth below. With respect to such examination, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as reproduced or certified copies, and the authenticity of the originals of those latter documents. As to questions of fact material to this opinion, we have, to the extent deemed appropriate, relied upon representations of certain officers of the Company.

Based upon the foregoing, we are of the opinion that:

The opinions we express above are based upon a review only of those laws, statutes, rules, ordinances and regulations which, in our experience, a securities lawyer who is a member of the bar of the State of New York and practicing before the Commission exercising customary professional diligence would reasonably recognize as being applicable to the foregoing transactions. In addition, we have assumed that the effectiveness of the Domestication Merger will result in the Company assuming all rights, duties and obligations of Parent under the Warrant Agreement by operation of the Business Companies Act (Revised Edition 2020), as amended, of the British Virgin Islands.

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The opinion set forth in paragraphs 2 above is subject to (i) the effect of any applicable bankruptcy, insolvency, reorganization, moratorium or similar law relating to or affecting creditors’ rights generally (including, without limitation, fraudulent conveyance laws) and (ii) the effect of general principles of equity, including, without limitation, concepts of materiality, reasonableness, good faith and fair dealing and the possible unavailability of specific performance or injunctive relief, regardless whether considered in a proceeding in equity or at law.

We express no opinion as to the enforceability of (i) provisions that relate to choice of law, forum selection or submission to jurisdiction (including, without limitation, any express or implied waiver of any objection to venue in any court or of any objection that a court is an inconvenient forum) to the extent that the validity, binding effector enforceability of any such provision is to be determined by any court other than a state court of the State of New York or (ii) waivers by the Company of any statutory or constitutional rights or remedies. We draw your attention to the fact that, under certain circumstances, the enforceability of terms to the effect that provisions may not be waived or modified except in writing may be limited.

The opinions we express herein are limited to matters involving the internal laws of the State of New York and the applicable provisions of the General Corporation Law of the State of Delaware. We express no opinion with respect to any other laws.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the reference made to us under the caption, “Legal Matters,” in the Registration Statement and in the prospectus constituting a part of the Registration Statement. In giving this consent, we do not hereby admit that we are in the category of persons whose consent is required under Section 7 of the Act, or the rules and regulations promulgated thereunder or Item 509 of Regulation S-K promulgated under the Act.

Very truly yours,